I don't want to have a debate over scripture so I won't cite scripture too much, in fact I will try to avoid it as much as possible. What I ma discussing is my view of self-defense as a Christian. My view may not be your view, but my view is based on both scripture and my own interpenetration of scripture. We all know Mathew 5:39 about no resisting evil with evil and turning the other cheek. Many see this as a call to pacifism. I however do not, how can the same God which instructed Israel to kill and battle the Canaanites also not instruct us to defend ourselves.
The answer is found in the context of the subject, objectivity in Luke 22:36 shows Jesus instructing his followers to sell their coats & buy swords. Yet when one of the disciples cut off a slaves ear in the garden of Gethsemane, Jesus healed the slave he said "Those who live by the sword, die by the sword." Mathew 26:52 and Jesus said in Mathew 26:56 "all this was done that the scripture of the Prophets might be fulfilled."
So the disciples were to be armed but not use the arms to defend Jesus because of his special role in God's plan. This merely shows that weapons are not forbidden to Christians. In Luke 22:35 Jesus references a task were he sent out his followers without shoes, money, swords or bags to preach the gospel. This was also to show that God's protection extended beyond Jesus, for those disciples laced nothing. In Luke 22:36 he then says "He said to them, “But now let the one who has a moneybag take it, and likewise a knapsack. And let the one who has no sword sell his cloak and buy one. (English Standard Version)" Here Christ knows he will be arrested and here he instructs his disciples to prepare, including being armed.
When Peter strikes a slave, Jesus tells him to put away the weapon. Saying those who live by sword (those who live a life of violence) die by the sword (die violently). So relying on violence is not permitted but being armed is. More so, to look at the verse John 15:13 Christ teaches us "No one shows greater love than when he lays down his life for his friends." (International Standard Version). But does laying down your life involve defending yourself or others?
It is important to understand why Christ came to earth. He came to teach the proper interpenetration of the scriptures, not just blindly following the law but that the law pointed one to follow the spirit. The bible is full of people David, Samson, Gideon and others were warriors. In my view Jesus instruction to be armed is simple, self-defense in implied. Because the slave did not attack anyone and Peter attacked he did two things wrong. First, the old testament view of self-defense (an eye for an eye) was never broken. No one was initially attacked, so no one had cause to defend themselves. Secondly, Jesus was to die for our sins as foretold by old testament prophets. Remember Jesus said he came to fulfill the law in Matthew 5:17. Surely this includes the law of self-defense?
But, Jesus said "turn the other cheek." He did but there is a difference between someone bitch slapping you (an insult) and someone trying to seriously hurt you. The thing is the bible also instructs a Christian to let others to steal from you. The bible allows you to defend yourself and calls on you to defend others. You are not to defend property (the things of this world) or the use violence to get what you want. You are to defend your life and the lives of those who cannot defend themselves, you are not return insult for insult, violence is limited to self-defense and self-defense limited to the extremes of intent to do you harm.
Sociology teaches us, that the human mind is hardwired to react in four ways; posturing with threat displays (which the Christian is instructed to avoid), fight (only to defend life and to go no further then the intended harm, hence "eye for an eye"), flight (which the Christian is called to do to avoid danger) and submission (which the Christian is called to do unless their very life is threatened immediately). And bible teaches us to follow a path of least resistance. Some Christians are called to be lions to defend others, wolves in sheep's clothing as it were, to fight when urgently needed. Others are called to be teachers, so that the lions do not exceed by force alone. Self-defense is not forbidden, it is permitted by only within the limits of the force used against you. Should you be attacked and no greater injury result then your wounded pride, you may wound no more then your attacker's pride. If an attacker tried to kill you, scripture offers a bit f gray area, you may defend yourself within the immediate need to preserve your life by killing the attacker. However, (this is a very important "However") once the threat has ended so has the need for self-defense and the use for violence.