If the Ten Commandments say “thou shalt not kill” how can a Christian fight in a war?

The breadth of Jesus' message is that if we found ourselves in any position that we thought killing would be OK - The correct response would be to actually love that person instead.

The life of the human body is irrelevant to the eternal life of the spirit.

** We are to Kill the spirit of evil in that person with love. **

(Don't forget, evil spirits are transferable and contagious.)

This doesn't mean that if they will continue to be a danger to others that they can't be locked up but to kill is the enemy winning.

To love is God winning.

A thief comes to steal, kill, and destroy. But I came to give life—life that is full and good.

-John 10:10

"Moses gave you the law, right? But you don’t obey that law. If you do, then why are you trying to kill me?” -Jesus - John 7:18

Matthew 10:28 (NET)

Do not be afraid of those who kill the body but cannot kill the soul. Instead, fear the one who is able to destroy both soul and body in hell.

The life of the human body is irrelevant to the eternal life of the spirit.

The other answers here are earthly perspectives.

Which would you rather be - enter the next world from natural causes a few years after killing your enemy or enter the next world killed by your enemy but without murder on your hands ??

Jesus died for His enemies. We are suppose to be little Christs.

Luke 9:55: http://www.biblestudytools.com/commentaries/gills-exposition-of-the-bible/luke-9-55.html

But he turned and rebuked them.
He turned himself about to them, and looking upon them with a stern countenance, sharply reproved them for their intemperate zeal, their passion of wrath, and anger, and desire of revenge:

and said, ye know not what manner of spirit ye are of;
or do not consider that this is not the true spirit of zeal, but of anger and revenge; and is not agreeable to the spirit of the meek and humble followers of Christ, or to the Spirit of God, and those gifts of his bestowed on them, nor to the spirit of the Gospel dispensation: so good men, for want of attention, may not know sometimes from what spirit they act; taking that for a good one, which is a very bad one; being covered with specious pretenses of love and zeal, and the examples of former saints; not observing the difference of persons; times, and things.

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Love Your Enemies

27 “But I say to you people who are listening to me, love your enemies. Do good to those who hate you. 28 Ask God to bless the people who ask for bad things to happen to you. Pray for the people who are mean to you. 29 If someone hits you on the side of your face, let them hit the other side too. If someone takes your coat, don’t stop them from taking your shirt too. 30 Give to everyone who asks you for something. When someone takes something that is yours, don’t ask for it back. 31 Do for others what you want them to do for you.

32 “If you love only those who love you, should you get any special praise for doing that? No, even sinners love those who love them! 33 If you do good only to those who do good to you, should you get any special praise for doing that? No, even sinners do that! 34 If you lend things to people, always expecting to get something back, should you get any special praise for that? No, even sinners lend to other sinners so that they can get back the same amount!

35 “I’m telling you to love your enemies and do good to them. Lend to people without expecting to get anything back. If you do this, you will have a great reward. You will be children of the Most High God. Yes, because God is good even to the people who are full of sin and not thankful. 36 Give love and mercy the same as your Father gives love and mercy.

Luke 9

23 Jesus continued to say to all of them, “Any of you who want to be my follower must stop thinking about yourself and what you want. You must be willing to carry the cross that is given to you every day for following me. 24 Any of you who try to save the life you have will lose it. But you who give up your life for me will save it. 25 It is worth nothing for you to have the whole world if you yourself are destroyed or lost. 26 Don’t be ashamed of me and my teaching. If that happens, I[a] will be ashamed of you when I come with my divine greatness and that of the Father and the holy angels. 27 Believe me when I say that some of you people standing here will see God’s kingdom before you die.”

Sorry but this commandment means exactly what it says.

God and Jesus are telling us not to take life in any context or situation.

God is all powerful and perfect - if he want's someone gone He can do it himself, He can wipe out an entire continent or the world with a flood if needed. I don't think I need a reference for that one.

With that said, why would we think we need to kill any one in any context, innocent, non-innocent, enemy, friend, slay in war, etc.

That would be taking the matter into our own hands and not trusting God.

God can change a killing situation in a second:

"For the word of God is quick, and powerful, and sharper than any two edged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart." (Hebrews 4:12 KJV).

God is also trying to protect us from being killed:

Then said Jesus unto him, Put up again thy sword into his place: for all they that take the sword shall perish with the sword (Matthew 26:52, King James Version)

The commandment is also reiterated from Jesus' mouth. Matthew 19: 16-18

16 A man came to Jesus and asked, “Teacher, what good thing must I do to have eternal life?”

17 Jesus answered, “Why do you ask me about what is good? Only God is good. But if you want to have eternal life, obey the law’s commands.”

18 The man asked, “Which ones?”

Jesus answered, “‘You must not murder anyone, you must not commit adultery, you must not steal, you must not tell lies about others, 19 you must respect your father and mother,’[e] and ‘love your neighbor[f] the same as you love yourself.’[g]”

He says:

Exodus 20:13 (KJV) Thou shalt not kill.

Notice that there are no unless, or if this, or that...etc.

The Old Testament commands to fight wicked nations, but that does not apply in the New Testament. For example,

The Catholic Church teaches that the Law of Moses (the Old Law) is a preparation for the Gospel, and as such no longer binding. The New Law (the Law of Gospel) is a perfection of it, given through faith in Christ.

And here is an example of a perfect part: Jesus specifically tells us at the Sermon on the mound we should not stand up for ourselves and that we should pray for such people. When Jesus returns He will then take care of the wicked or will call us to help Him. It is very hard to accept. (Do I personally think I could do it in all situations, I do not know...but looking at Jesus the answer is there.)

We forget Jesus IS GOD - FROM GODS MOUTH: read carefully:

You have heard that it was said, 'An eye for an eye, and a tooth for a tooth.' But I say to you, do not resist an evil person; but whoever slaps you on your right cheek, turn the other to him also. If anyone wants to sue you and take your shirt, let him have your coat also. Whoever forces you to go one mile, go with him two. Give to him who asks of you, and do not turn away from him who wants to borrow from you. You have heard that it was said, 'You shall love your neighbor and hate your enemy.' But I say to you, love your enemies and pray for those who persecute you. (Matthew 5:39-44)

Doesn't leave much room for killing. Some say it is Jesus using a hyperbole but if He was he would have said so.

Even "violent white KKK Christians" are leaning more towards what Jesus was trying to say here:

"Odinism has lately gained in popularity among white supremacists who believe that Jesus is too peaceful and too Jewish to worship, White said. "It's hard to get a violent god out of Jesus."

As followers in Christ, we do not belong to any country, we belong to our Lord. We are told to obey them but not if it contradicts the word of God.

So being a Christian and in the Military IN A POSITION OF KILLING is not really a Christian concept. There are may Christians who during WWII refused to carry a weapon and were pushed into medical care and other service positions.

Exodus 20:13 does mean Thou shalt not Kill.

But this only applies for moral reasons.

This doesn't apply against wicked reasons and self defense.

God ejected Canaanites out of their land through Israelites, because of their wickedness (Leviticus 18:24-28, Deuteronomy 9:4-5).

David Kills Goliath in 1 Samuel 17. David Killed Goliath, because Philistines came for war against Israel. So Israel had to defend themselves.

On the top of that, Goliath was an egotistical man and cursed David by his gods (1 Samuel 17:41-44). As David points out in 1 Samuel 17:45, Goliath defied God. So with the help of God, David killed Goliath (1 Samuel 17:50).

Jesus Christ called his generation "Wicked and Adulterous generation" (Matthew 16:4, Mark 8:38). That's why he prophesied the destruction of Jerusalem (in Matthew 24, Mark 13, and Luke 21) which occurred in 70 AD through Titus and his Roman Army as explained by Josephus in his word Jewish Wars (especially Book Six).

I was just studying this. If you read more about this very topic you'll find that God is talking about shedding innocent blood.

Have a look at what God did here:

Judges 3:1-2 (New International Version)

1 These are the nations the LORD left to test all those Israelites who had not experienced any of the wars in Canaan

2 (he did this only to teach warfare to the descendants of the Israelites who had not had previous battle experience):

God literally preserved wicked nations around Israel just to teach the Israelite's how to fight. Have a look at this other command straight from Jesus.

Luke 22:36 (New International Version)

36 He said to them, “But now if you have a purse, take it, and also a bag; and if you don’t have a sword, sell your cloak and buy one.

Jesus is telling us to carry a sword with us when we go out to preach his word. God is not a pushover. God is a man's man that is very capable of sending you into battle, so that you may bring Him glory.

When you hear preachers saying that soldiers need to repent, well, that preacher needs to read his Bible and come to terms with the fact that God is the General of His people.

There are two ways to approach that commandment. Either it is absolute or it is relative: it can either refer to all of human life, or some subset of human life. Clearly it cannot be the former as the Torah also allows for the death penalty (before anyone tries to argue, "but Christ says..." or "but the woman caught in adultery..." I will counter that the original question is in reference to the 10 Commandments and their context must be the first place we look for the intended meaning). Therefore it must be some sub-set of humans who should not be killed. We also know (similarly from the Torah) that there were circumstances where war was acceptable, so the original, intended meaning of the commandment cannot be said to include war.

Based off of the penal laws of the Old Testament, it actually becomes fairly clear that "kill" here, for a private citizen, must mean wrathfully and willfully (Exo. 21:14) or through negligence (c.f. Exo. 21:28). However, if the person is caught in the commission of a crime, that "killing" is licit (Exo. 22:1). As far as a society is concerned, however, it is clear that both the death penalty and war are not only permitted, but at times even encouraged.

Now, to bring this forward to Christianity. While we cannot deny the admonitions to "turn the other cheek", "he who is without sin", and "he who lives by the sword", it should be noted that there is nothing which actually condemns the legitimate defense of one's household and property. If anything, Christ's use of a whip to injure (what else would the whip do?) the money-lenders in the temple should be seen as an expression that sometimes violence is not only justified, but necessary (Christ always did the best thing, overturning the tables and making a whip, therefore, must have been the best thing).