What is unique about Christianity?

One aspect of Christianity that seems small but important is:

Luke 6:31 (NIV) Do to others as you would have them do to you.

Other religions (that I know about) say something like:

Don't do to others what you don't want them to do.

(A nice list of a few teachings shows us this "Inverse Golden Rule" or I remember hearing it called "the Silver rule".) EDIT:- as this seems to be an issue that people are not quite understanding what I initially intended to say I will elaborate: The Christian "Golden Rule" is to do good to others and the inverse of this is not to do harm to others. If you know of a religious text that is not Christian and states the Golden Rule then please correct me. With the Golden Rule one would look for opportunities to do good in peoples lives as a proactive approach. The Inverse Golden Rule makes us stop and think "Is this going to harm?".

While this may not seem like a big difference but it ties into the second greatest commandment:

Matt 22:39 (NIV) Love your neighbour as yourself.

EDIT 2:- At this point the post is -4 so I understand most people won't even look this far down but I still think the distinction needs to be made. The difference from Jesus's teaching compare to others is a permissive (or pro-active) command: "Go do good" is different to the don't do/wish harm on others. In this I Haven't taken in Judaism as a separate religion as Jesus, being a rabbi, would have taught from this point. Taoism:

“Regard your neighbor’s gain as your own gain and your neighbor’s loss as your own loss.”

This is not the Pro-active position Jesus taught from, is is a passive one. (Passive as in there is no action here other than to "regard".)

On a broader look of the Bible you see it as the only (Someone correct me if I am wrong) religious text that tells of what God (or whatever deity) did to reconcile man to himself rather than what man needs to do to reconcile himself to his deity. The core of what Christianity is: Jesus died for us, rather than what we have to do to be made right.

The most fundamental truth that distinguishes Christianity is the belief in trinity. God the Father, God the Son and God the Holy Spirit. Some religions like Islam, believe in the Unity of God (oneness). Magian's Duality of God and other varieties of all other religions.

I find Christianity to be unique, speaking philosophically, in its emphasis on the idea that God loves us in a personal way as individuals --as evidenced by parables such as the widow and the coins, the prodigal son, the shepherd and the lost sheep, the sparrow with the numbered feathers, and so forth. In such parables, Jesus teaches that it makes a difference to God to lose any single one among us.

I know of no other religion that establishes the same principle of a direct connection between the most universal, eternal, perfect and holy of all beings, and the specific, mortal, flawed and profane existence of we individual human beings. Only Christianity makes the radical claim that the latter is considered of crucial importance by the former.

I agree with comments made by David Stratton, Caleb, Peter Turner, and Neil Meyer. But let me add one more point:

The question says that Christianity is like many other religions in that "CLAIMS to speak on behalf of God", "CLAIMS to be historically accurate", "CLAIMS to be the one true religion", etc. This may well be true, but the important question is not who CLAIMS to be telling the truth, but who IS telling the truth.

If one person who calls himself a doctor says that he thinks the way to cure cancer is with radiation therapy, and another says that the proper treatment is with changes to diet, and a third says that the right way is by dying your hair blue and bathing in motor oil, would you say that because all of them CLAIM that their treatment is scientific and effective that therefore all are basically the same and should be given the same credence? Surely not. Surely what is important is what evidence they can produce to back up their claims.

There's already plenty of answers for this...but no answer by way of parable :)

Imagine you had too much to drink and somehow ended up in the middle of the ocean and you're drowning. The waves are too high and rough. What's more is you don't know how to swim--you're going to die. Suddenly, a boat drives up near you and throws you a flotation-ring. At the same time, another boat pulls up to you and the driver of that second boat just starts yelling at you: "Swim harder! Try harder! You can do it without the flotation ring!"

The driver of the former boat represents Jesus Christ. Jesus sees that you're going to die and saves you.

The driver of the latter boat represents religion, even those masquerading with the label of "Christianity". As long as you try your best you'll be saved in the end--but it turns out to be a big lie because your best just isn't good enough.

The ocean represents sin. We're surrounded by it and it's killing us. We can't escape it and it's our own fault for being there. Jesus says the only thing we need to do is place our faith in HIM for salvation (taking the floaty). Religion says if you do enough good deeds (swimming harder) you'll be fine in the end, but it ends up being a lie. Some people (atheists) are in the middle--too proud to take the floaty and too proud to listen to the 2nd driver, but they end up drowning anyway.

When asked the question, CS Lewis responded "Oh, that's easy. It's grace."

Christianity is the only religion that is not a religion.

It is an encounter with the Person of Jesus Christ.

Being Christian is not the result of an ethical choice or a lofty idea, but the encounter with an event, a person, which gives life a new horizon and a decisive direction.

Deus Caritas Est

I think the main thing that makes Christianity unique is that it is a Story about God taking on human form and dwelling among us. Not "merely" a prophet, but Emanuel. And this Story turns the concept of power on its head, where God-dwelling-among-us is the Suffering Servant that lays his life down for, not just "friends", but even enemies (that he loves). The Story tells us how God really loves us and teaches, with sermon and example, how we can really love God and love others.

I think that Story is unique. Not every element, but some elements are unique and the sum-total of the elements of the Story is unique.

[1 Tm 3:16] Great indeed, we confess, is the mystery of our religion:

He was manifested in the flesh, vindicated in the Spirit, seen by angels, preached among the nations, believed on in the world, taken up in glory.

[The Doctrine of] Divine Filiation: the calling to be sons in the Son, and calling God, Abba, Father, is unique about Christianity.

In other religions, mortals craved to be sons of the gods, or strove to be [declared] gods after death [and only a few, the legendary, could achieve it], or worse, were themselves gods.

In Christianity, a free gift is on offer.

See what love the Father has given us, that we should be called children of God; and so we are. [...] Beloved, we are God’s children now; it does not yet appear what we shall be, but we know that when he appears we shall be like him, for we shall see him as he is. [1 Jn 3: 1-3]

The Father, who has no need of us, nor of our praise, has an Only Son in whom is ALL his delight. Through that Son, he called us into being, and not stopping at that, after redeeming us, raised up to the dignity of children of God; and when the Spirit of his Son has fully formed us into the image of his Son, he loves in us what he sees and loves in Christ [cf. 'so that you might love in us what you loved in your Son' | Preface VII of Sundays in Ordinary Time | The Eucharistic Prayer | The Liturgy of the Eucharist | The Order of [Catholic] Mass].

This is mind-boggling: 'the things which have now been announced to you by those who preached the good news to you through the Holy Spirit sent from heaven, things into which angels long to look.' [cf. 1 Pt 1:12]

To see God as he sees himself, to love him with his own love and as he loves himself, and to live with his own life: to participate in the Divine Nature [cf. 2 Pt 1:4].

Please see St. Paul on this as well e.g. Rm 8:14-17 and Gal 4:4-7:

For all who are led by the Spirit of God are sons of God. For you did not receive the spirit of slavery to fall back into fear, but you have received the spirit of sonship. When we cry, “Abba! Father!” it is the Spirit himself bearing witness with our spirit that we are children of God, and if children, then heirs, heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him.

and

But when the time had fully come, God sent forth his Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons. And because you are sons, God has sent the Spirit of his Son into our hearts, crying, “Abba! Father!” So through God you are no longer a slave but a son, and if a son then an heir.

According to the Bible, God was in the beginning and was the only God worshiped as such. He revealed Himself to Adam and Noah specifically. At Babel, the people of the earth were divided by language, yet all of them retained some history and understanding of God's interactions with mankind in the world that is recorded in Genesis 1-11. From this, we should expect to find similar rituals that match up to those accounts.

In fact, we find just that. In his book, Eternity in their Hearts, Don Richardson records peoples all over the world with "strange traditions" that mirror the concepts of sacrifice, atonement, etc. The Chinese alphabet also has remarkable ties back to Genesis. So, cultures scattered all over the world do share some commonalities with Christianity and Genesis.

However, the similarities of religion are quite small. To quote Malcolm Muggeridge:

We believe that all religions are basically the same– at least the one that we read was. They all believe in love and goodness. They only differ on matters of creation, sin, heaven, hell, God, and salvation

Religions do often have very close similarities when it comes to ideas of morality, and the Bible indicates that God's law is written on our hearts. So, that makes sense.

Religions, however, differ greatly on a number of things, including the nature of God, the Person of Jesus, and what man must do with his sins.

The Nature of God

Christianity has a unique concept of God, which is shared in part by Judaism and to a much lesser degree by Islam. In Christianity, man is created in the image of God, whereas in many other religions, God is created in the image of man. An example of this is Greek mythology, which attributed sexuality and such to divine beings.

The Person of Jesus

Another very significant distinction that makes Christianity unique is its answer to the question, "Who is Jesus?" In some religions, men may become gods, but in Christianity, God became a Man and entered into His own creation.

What Man Must Do With His Sin

Finally, what man must do with his sin is perhaps the most unique aspect of Christianity. In Christianity, we have committed sins, and God is just. Sins must be paid for. However, man may not ever pay his own debt for his own sins. In all other religions, a man must do penance of some sort. The idea that if your good outweighs your bad, then you're heaven bound. This idea, though, leaves sins unpunished, and it's based on man making amends for his own sin--just like Adam and Eve trying to cover over the shame of their own sin in the garden. Just as it was in the garden, so it is now that man may not cover over his own sin.

Christianity is based on God reaching down to man and making a complete payment for man's sins once for all through the death and resurrection of Jesus Christ. It is based on a free gift that makes no demands of penance on the individual. A Christian is expected to do good deeds not out of his own will, but out of the transformation that God has worked in his heart upon his faith in Jesus.

One way to put it is that all other religions bid the lame man walk, whereas Christianity heals the lame man so that he can walk.

As an aside, the Bible is quite unique as it is the only sacred text that dares to set forth many specific predictive prophecies that come true hundreds of years later. The year that Messiah was to come was even specified.

Conclusion

So, the answers to the three questions are what make Christianity unique:

1. Who is God? He is the transcendent creator of the universe, one God in Three Person, whose image we bear (one person with body, soul and spirit). Men are made in the image of God, but God is not in the image of man.

2. Who is Jesus? He is the eternal Son of God who entered into creation about 2,000 years ago to fulfill the prophecies recorded in the Old Testament. He died on the cross, rose on the third day, and ascended into heaven as King of Kings and Lord of Lords. Men do not become gods, but God did become a man.

3. What must man do with this sin? Rather than having to work our own way to heaven in order for our sins to not be paid for, but outweighed by good deeds, Christianity teaches that God reaches down to man and provides a complete payment for his sins. We, therefore, stand before God as sinners who are declared righteous. With our debt paid, no one may lay any claim against us, because the debt is fully satisfied. Christians can have complete confidence in this, whereas followers of other religions seldom have any confidence that their good outweighs their bad.

This is a question that requires a long quote to be read, in context, from Chesterton's Orthodoxy, you really should read the entire book, but you may be able to pick up a few chestnuts here or there from this excerpt:

The things said most confidently by advanced persons to crowded audiences are generally those quite opposite to the fact; it is actually our truisms that are untrue. Here is a case. There is a phrase of facile liberality uttered again and again at ethical societies and parliaments of religion: "the religions of the earth differ in rites and forms, but they are the same in what they teach." It is false; it is the opposite of the fact. The religions of the earth do not greatly differ in rites and forms; they do greatly differ in what they teach. It is as if a man were to say, "Do not be misled by the fact that the CHURCH TIMES and the FREETHINKER look utterly different, that one is painted on vellum and the other carved on marble, that one is triangular and the other hectagonal; read them and you will see that they say the same thing." The truth is, of course, that they are alike in everything except in the fact that they don't say the same thing. An atheist stockbroker in Surbiton looks exactly like a Swedenborgian stockbroker in Wimbledon. You may walk round and round them and subject them to the most personal and offensive study without seeing anything Swedenborgian in the hat or anything particularly godless in the umbrella. It is exactly in their souls that they are divided. So the truth is that the difficulty of all the creeds of the earth is not as alleged in this cheap maxim: that they agree in meaning, but differ in machinery. It is exactly the opposite. They agree in machinery; almost every great religion on earth works with the same external methods, with priests, scriptures, altars, sworn brotherhoods, special feasts. They agree in the mode of teaching; what they differ about is the thing to be taught. Pagan optimists and Eastern pessimists would both have temples, just as Liberals and Tories would both have newspapers. Creeds that exist to destroy each other both have scriptures, just as armies that exist to destroy each other both have guns.

On the surface religions looks the same, just as on the surface people look the same.

The great example of this alleged identity of all human religions is the alleged spiritual identity of Buddhism and Christianity. Those who adopt this theory generally avoid the ethics of most other creeds, except, indeed, Confucianism, which they like because it is not a creed. But they are cautious in their praises of Mahommedanism, generally confining themselves to imposing its morality only upon the refreshment of the lower classes. They seldom suggest the Mahommedan view of marriage (for which there is a great deal to be said), and towards Thugs and fetish worshippers their attitude may even be called cold. But in the case of the great religion of Gautama they feel sincerely a similarity.

People often make a thesis statement saying, 'all religions are the same' but follow up with 100 reasons they're different or they pick and choose the parts that are 'all the same'.

Students of popular science, like Mr. Blatchford, are always insisting that Christianity and Buddhism are very much alike, especially Buddhism. This is generally believed, and I believed it myself until I read a book giving the reasons for it. The reasons were of two kinds: resemblances that meant nothing because they were common to all humanity, and resemblances which were not resemblances at all. The author solemnly explained that the two creeds were alike in things in which all creeds are alike, or else he described them as alike in some point in which they are quite obviously different. Thus, as a case of the first class, he said that both Christ and Buddha were called by the divine voice coming out of the sky, as if you would expect the divine voice to come out of the coal-cellar. Or, again, it was gravely urged that these two Eastern teachers, by a singular coincidence, both had to do with the washing of feet. You might as well say that it was a remarkable coincidence that they both had feet to wash. And the other class of similarities were those which simply were not similar. Thus this reconciler of the two religions draws earnest attention to the fact that at certain religious feasts the robe of the Lama is rent in pieces out of respect, and the remnants highly valued. But this is the reverse of a resemblance, for the garments of Christ were not rent in pieces out of respect, but out of derision; and the remnants were not highly valued except for what they would fetch in the rag shops. It is rather like alluding to the obvious connection between the two ceremonies of the sword: when it taps a man's shoulder, and when it cuts off his head. It is not at all similar for the man. These scraps of puerile pedantry would indeed matter little if it were not also true that the alleged philosophical resemblances are also of these two kinds, either proving too much or not proving anything. That Buddhism approves of mercy or of self-restraint is not to say that it is specially like Christianity; it is only to say that it is not utterly unlike all human existence. Buddhists disapprove in theory of cruelty or excess because all sane human beings disapprove in theory of cruelty or excess. But to say that Buddhism and Christianity give the same philosophy of these things is simply false. All humanity does agree that we are in a net of sin. Most of humanity agrees that there is some way out. But as to what is the way out, I do not think that there are two institutions in the universe which contradict each other so flatly as Buddhism and Christianity.

Others just stretch the truth to the point that both religions resemble each other because they're seen so dimly that they don't really resemble anything

Even when I thought, with most other well-informed, though unscholarly, people, that Buddhism and Christianity were alike, there was one thing about them that always perplexed me; I mean the startling difference in their type of religious art. I do not mean in its technical style of representation, but in the things that it was manifestly meant to represent. No two ideals could be more opposite than a Christian saint in a Gothic cathedral and a Buddhist saint in a Chinese temple. The opposition exists at every point; but perhaps the shortest statement of it is that the Buddhist saint always has his eyes shut, while the Christian saint always has them very wide open. The Buddhist saint has a sleek and harmonious body, but his eyes are heavy and sealed with sleep. The mediaeval saint's body is wasted to its crazy bones, but his eyes are frightfully alive. There cannot be any real community of spirit between forces that produced symbols so different as that. Granted that both images are extravagances, are perversions of the pure creed, it must be a real divergence which could produce such opposite extravagances. The Buddhist is looking with a peculiar intentness inwards. The Christian is staring with a frantic intentness outwards. If we follow that clue steadily we shall find some interesting things.

The uniqueness of Christianity is the perspective that a Christian has! Other religions are inward facing, Christianity is the only one that is completely outward facing.

It is just here that Buddhism is on the side of modern pantheism and immanence. And it is just here that Christianity is on the side of humanity and liberty and love. Love desires personality; therefore love desires division. It is the instinct of Christianity to be glad that God has broken the universe into little pieces, because they are living pieces. It is her instinct to say "little children love one another" rather than to tell one large person to love himself. This is the intellectual abyss between Buddhism and Christianity; that for the Buddhist or Theosophist personality is the fall of man, for the Christian it is the purpose of God, the whole point of his cosmic idea. The world-soul of the Theosophists asks man to love it only in order that man may throw himself into it. But the divine centre of Christianity actually threw man out of it in order that he might love it. The oriental deity is like a giant who should have lost his leg or hand and be always seeking to find it; but the Christian power is like some giant who in a strange generosity should cut off his right hand, so that it might of its own accord shake hands with him. We come back to the same tireless note touching the nature of Christianity; all modern philosophies are chains which connect and fetter; Christianity is a sword which separates and sets free. No other philosophy makes God actually rejoice in the separation of the universe into living souls. But according to orthodox Christianity this separation between God and man is sacred, because this is eternal. That a man may love God it is necessary that there should be not only a God to be loved, but a man to love him. All those vague theosophical minds for whom the universe is an immense melting-pot are exactly the minds which shrink instinctively from that earthquake saying of our Gospels, which declare that the Son of God came not with peace but with a sundering sword. The saying rings entirely true even considered as what it obviously is; the statement that any man who preaches real love is bound to beget hate. It is as true of democratic fraternity as a divine love; sham love ends in compromise and common philosophy; but real love has always ended in bloodshed. Yet there is another and yet more awful truth behind the obvious meaning of this utterance of our Lord. According to Himself the Son was a sword separating brother and brother that they should for an aeon hate each other. But the Father also was a sword, which in the black beginning separated brother and brother, so that they should love each other at last.

And Christianity is the only thing that can say this.

Orthodoxy - Chapter 8

I think there are two points you should take away, and I apologize for the long quote, but you're reading for your own wisdom so it would be fruitless to take away.

Point 1. That Christianity is sacrificial outwardly, I think other answers have touched on this

Point 2. That Christ would be a sign which would be contradicted. Other gods test their progeny, but I don't think any set them up to fail and die on a cross. Other gods unite households under their protection, only Christianity specifically sets out to turn father against son.

Christianity is unique in being the only religion in the history of the world to turn the tables on man (in every sense). It stands apart in its claim to reconcile a perfectly just God as being both just and the justifier of unjust men.

Christianity stands alone in being the only religion whose God gave up his rights –and very life– on behalf of his constituents. It alone is not a system whereby men, through any contrivance at all, is ever able to reach God but only ever demonstrates his utter failure to do so. Instead, God came to men—to the point of surrendering himself to death at the hands of the very people he purposed to save—in order to show just how backwards this religion was.

The legions of men who blithely assert that all religions lead to God in the end are right in this: that the many varied roads mapped and traveled by men in their attempt to reach God merely merge into one wide way. The exception invariably overlooked is Christ: the narrow road that God mapped and traveled to reach lost men. — Myself

Christianity is without parallel in its claim that men can do nothing good apart from God's intervention. And yet this is still one of the single largest struggles inside Christianity as men wrestle with the idea that they still, through some power of their will or collection of deeds, effect their own salvation.

A man's 'free'-will cannot cure him even of the tooth ache, or of a sore finger; and yet he madly thinks it is in its power to cure his soul. — Augustus Toplady

Lastly, Christianity has a key feature in the Resurrection. No-one else in history has had the authority to lay down their life and take it up again.