What is the essence of sin?

The essence of Sin is to act contrary to to Love. It has been said above but it can not be said enough. The Savior said it best here:

Matthew 22:37-40 (ESV)
37 And he said to him, "You shall love the Lord your God with all your heart and with all your soul and with all your mind. 38 This is the great and first commandment. 39 And a second is like it: You shall love your neighbor as yourself. 40 On these two commandments depend all the Law and the Prophets."

If you have perfect Love for your fellow man you will have no desire to sin, and will keep all the commandments perfectly. We best Love and serve God by keeping his commandments which are to Love and serve others.

John 14:15
15 If ye love me, keep my commandments.

Sin is trangressing the law, which is summarized by love thy neighbour as thyself.

8 Owe no man any thing, but to love one another: for he that loveth another hath fulfilled the law. 9 For this, Thou shalt not commit adultery, Thou shalt not kill, Thou shalt not steal, Thou shalt not bear false witness, Thou shalt not covet; and if there be any other commandment, it is briefly comprehended in this saying, namely, Thou shalt love thy neighbour as thyself. Romans 13:8-9

See also Matthew 22:37-40; 1 John 3

This is a good question with no direct answer in the Bible. But we get a good glimpse of it's "essence" in the following scripture:

Let no one say when he is tempted, "I am tempted by God"; for God cannot be tempted by evil, nor does He Himself tempt anyone. But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death. James 1:13-15

I think we see here that there is a definite process that begins before sin is committed and then after sin is committed. The above answers do really well to highlight those things, and so I will emphasize a couple of things

-Sin starts with pride - one's "own desires" that are not shared with God. -Sin is born, presumably when they are committed, but after that, they can develop into something worse. Jesus might be alluding to this in John 5:14 when he says, "Go and sin no more lest a worse thing befall you." -Sin does not come from God. It is apart from Him, distinct from Him, and what ever nature or essence it has is not shared with God

Selfishness.

The essence of sin is selfishness. Let me explain.

The first of the Ten Commandments tells us not to have other gods beside God ¹. God is God, and man is man. There's a huge difference. God deserves all the glory (Job 38-40); man deserves nothing but death (Romans 6:23). God will not give his glory away, either ².

What originally tempted humans to choose sin was the promise to be like God ³. This is selfishness; instead of giving glory to God, wanting to be as glorious as God is. Like Adam and Eve, we often want glory for ourselves instead of giving it to God, who deserves it ⁴. This is selfishness, and it is sin.

Now, here's an important passage:

Matthew 22:37-40 (ESV)
³⁷ And he said to him, "You shall love the Lord your God with all your heart and with all your soul and with all your mind. ³⁸ This is the great and first commandment. ³⁹ And a second is like it: You shall love your neighbor as yourself. ⁴⁰ On these two commandments depend all the Law and the Prophets."

Here, Jesus tells us what the essence of the Law and the Prophets is. It is to love God and other people. The neglect of loving others is selfishness; the neglect of Law is sin. What, then, is the ultimate selfishness? It's being so self-righteous that we don't even confess that we need help ⁵. That's also the ultimate sin; refusing salvation.

1. Exodus 20:2-3 (ESV)
   ² "I am the LORD your God, who brought you out of the land of Egypt, out of the house of slavery.
   ³ "You shall have no other gods before me.

2. Isaiah 48:11 (ESV)
   For my own sake, for my own sake, I do it,
      for how should my name be profaned?
       My glory I will not give to another.

3. Genesis 3:4-5 (ESV)
   ⁴ But the serpent said to the woman, "You will not surely die. ⁵ For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil."

4. John 7:18 (ESV)
   The one who speaks on his own authority seeks his own glory; but the one who seeks the glory of him who sent him is true, and in him there is no falsehood.

5. Mark 2:17 (ESV)
   And when Jesus heard it, he said to them, "Those who are well have no need of a physician, but those who are sick. I came not to call the righteous, but sinners."

The essence of sin is a rejection of God. We broke off our relationship with him.

God is the center of everything. He deserves all glory and honour as our creator and sustainer (Rev 4:11). He has the authority to say what we should do. Yet we think we know better and disobey his Word thinking we can be like him (Gen 3:5-6), we ignore him and pretend he doesn't exist (Rom 1:19), we prostitute ourselves with other gods (Ex 32, Mat 6:24).

This is why the gospel is primarily about being reconciled with God. It's not about getting into heaven, or finding meaning in life by finding God, or learning how to love one another. With these, there is still the problem of our broken relationship with God. Christ's death was to bring us forgiveness from God; redemption so we're no longer slaves to sin, but adopted to be his treasured children (Eph 1:1-14).

One of the best descriptions of sin that I have heard is, "Any disturbance of the shalom God intended for us." The problem with regarding sin as simple rule breaking is that keeping all the rules does not lead to the Kingdom of God.

Consider the Rich Young Ruler (Mark 10:17-27) for example. He asserts that he has kept the law since his youth and Jesus does not contradict him on this point. Instead, Jesus tells the man to go and sell everything he has and give to the poor. In other words Jesus is saying, "see there's not peace in this world, there are people in need. Stop hanging onto your stuff and help people." Or, as James puts it, "If anyone, then, knows the good they ought to do and doesn't do it, it is sin for them." (James 4:17)

Thus, sin is not just rule breaking, it is not being in line with what God is doing to advance his kingdom. This way of thinking about things brings so much freedom. We are freed from always worrying about making a misstep into sin and instead can focus on seeking to imitate Christ and listen to what God is doing in our world.

Here's one source for this kind of definition: http://robbellcom.tumblr.com/post/80913487032/what-is-the-bible-part-59-sin

There are different concepts of "sin" to be considered. For instance, Christians hold to the doctrine of a sinful nature--meaning all humans are sinful from birth, by virtue of the fact that they are human.

However, it seems your question is more along the lines of what actions (including thoughts) are sin.

I think a concise definition in this context would be "Acting against the will of God." Although to my knowledge, such a concise definition is not found in scripture. If you look at the various scriptures that define sinful acts, though, you can come up with this concise definition:

• Deliberate act against the law of God -- 1 John 3:4
• Mental consent to temptation -- Romans 7:7-8, Matthew 5:27-28, James 1:14, Proverbs 24:9
• Unbelief -- Romans 14:23, John 3:18, John 16:8-9
• Negligence or Failure to do good -- James 4:17, James 2:14, Matthew 23:23, Matthew 25:43-46
• Doing wrong out of ignorance -- Leviticus 5:17-19, Luke 12:48, 1 Timothy 1:13

At its most basic essence, sin is simply unbelief. The actions that we normally associate with sin (see Galatians 5:19-21) are only products of unbelief (the opposite of faith).

Romans 14:22-23 (KJV) Hast thou faith? have it to thyself before God. Happy is he that condemneth not himself in that thing which he alloweth. And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin.

I believe that Wesley best defined sin as "A willful transgression of a known law of God." Romans 5:13 says, "... before the law was given, sin was in the world. But sin is not taken into account when there is no law." Romans 7:7 says, "What shall we say, then? Is the law sin? Certainly not! Indeed I would not have known what sin was except through the law. For I would not have known what coveting really was if the law had not said, “Do not covet.”"

Therefore, I would have to agree with Wesley's conclusion that sin is doing something of which you know God doesn't approve.

The law was given so that we might know what sin was.

1 John 3:4 (NIV) Everyone who sins breaks the law; in fact, sin is lawlessness.

Romans 5:13 (NIV) To be sure, sin was in the world before the law was given, but sin is not charged against anyone’s account where there is no law.

1 John 5:17 (NIV) All wrongdoing is sin, and there is sin that does not lead to death.

And here's why there is no such thing as a good atheist.

Romans 14:23 (NIV) But whoever has doubts is condemned if they eat, because their eating is not from faith; and everything that does not come from faith is sin.

Because everything not of faith is sin.

Here's an opposing view of sin in order that you may further understand what it is.

Proverbs 16:6 (NIV) Through love and faithfulness sin is atoned for; through the fear of the LORD evil is avoided.

Love counters sin.

1 Peter 4:8 (NIV) Above all, love each other deeply, because love covers over a multitude of sins.

Wickedness is the Sin that Jesus demands we repent of. We are the first of all of God's creation to bear a new kind of fruit and that fruit is love. Any tree that does not bear good fruit will be cut down and thrown into the fire.

To quote the Westminster Shorter Catechism (Q 14, "What is sin?"):

Sin is any want of conformity unto, or transgression of, the law of God.

And the references given (Leviticus 5:17, James 4:17, 1 John 3:4):

And if a soul sin, and commit any of these things which are forbidden to be done by the commandments of the LORD; though he wist it not, yet is he guilty, and shall bear his iniquity.

Therefore to him that knoweth to do good, and doeth it not, to him it is sin.

Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.

Simply put, sin (lowercase s) is the act of disobeying God.

A bit more complexly put, Sin (capital S) is kind of like a disorder that Adam and Eve got from disobeying God and that we all inherited. This disorder (AKA our cursed flesh) contributes to our sinning, that is, committing sin, the act of disobeying God.

Requested Biblical references for original Sin:

Genesis 8:21

21 The LORD smelled the pleasing aroma and said in his heart: “Never again will I curse the ground because of humans, even though every inclination of the human heart is evil from childhood. And never again will I destroy all living creatures, as I have done.

Psalms 51:5

5 Surely I was sinful at birth, sinful from the time my mother conceived me.

Romans 3:10-12

10 As it is written:

“There is no one righteous, not even one; 11 there is no one who understands; there is no one who seeks God. 12 All have turned away, they have together become worthless; there is no one who does good, not even one.”

Romans 5:12

12 Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned

(All emphasis mine)

As to how this happened, I don't know how better to describe it other than "we inherited it".