Scriptural Principles of Self-Defense
The Bible instructs believers to turn the other cheek, to not resist an evil person, to bless those that persecute them, to never avenge themselves, and that all who take the sword will perish by the sword. How are we to understand these things? Is it man's moral duty to provide no defense for oneself and others? Rightly understood, the scriptures of the Old and New testaments provide sufficient cause for both the defense of self, and of others.
It should be obvious that the Bible doesn't speak specifically about firearms. It does speak about life, the taking of life, the defense of self and others, and the protection and provision of the weak and helpless.
Surely for your lifeblood I will demand a reckoning; from the hand of every beast I will require it, and from the hand of man. From the hand of every man’s brother I will require the life of man. “Whoever sheds man’s blood, By man his blood shall be shed; For in the image of God He made man.
God has created all things and has authority over all things. The image of God in man informs us that we have no authority to take life other than where God allows. The positive application of not committing murder is to protect life, which includes the life of ourselves and others. Commentary
You shall not murder.
As is the case with Genesis 9:5-6, the prohibition against murder shows us the importance of life and the protection of it. Not only do we learn with this verse to not take life unlawfully, but we also learn that we must protect life. Commentary
For more on this consult the Confessional Principles.
If the thief is found breaking in, and he is struck so that he dies, there shall be no guilt for his bloodshed. If the sun has risen on him, there shall be guilt for his bloodshed. He should make full restitution; if he has nothing, then he shall be sold for his theft.
One principle learned in this passage is that the use of violence is for the purpose of preserving life, and not safeguarding property. The two may at times be hard to distinguish, and a person taking or damaging your property, or seeking to enter your property, may well be ready and willing to injure you or others, and it may be proper to use force against the person, but to take up a weapon ought to always be for the purpose of the preservation of life. Shooting someone walking away with your TV and posing no physical harm to you or to others, if shot, has been murdered. The person robbing you of your TV, having the means to harm you, and seeking to do so, may have force used against him without you incurring bloodguilt. The issue here is not literally daytime versus nighttime, but the possibility of making a reasonable determination of the criminals intent. At least one commentator has pointed out, also, that the person entering at night is generally aware that he has a greater chance of encountering a resident, and therefore is more likely to be a violent criminal prepared to put down any resistance he encounters. Commentary
So it was, from that time on, that half of my servants worked at construction, while the other half held the spears, the shields, the bows, and wore armor; and the leaders were behind all the house of Judah. Those who built on the wall, and those who carried burdens, loaded themselves so that with one hand they worked at construction, and with the other held a weapon. Every one of the builders had his sword girded at his side as he built. And the one who sounded the trumpet was beside me.
God's people had the tools necessary for self-defense. They were watchful for threats and they carried with them weapons necessary to that defense. While some good commentators spiritualize this passage, "We must watch always against spiritual enemies," nevertheless the actual physical act of being prepared to defend against violence is inescapable here.
Defend the poor and fatherless; Do justice to the afflicted and needy. Deliver the poor and needy; Free them from the hand of the wicked.
This passage is focused on the magistrate and the need to provide true justice to all regardless of position and to make certain that the poor man doesn't go without proper defense, as he is one that can easily be abused. While it does not speak directly to a physical defense against aggression, or to individuals, nevertheless it establishes a principle that applies in all of life. Men ought to care for and seek to protect those that are weak, or poor, or unable to defend themselves. It is ensuring justice to save a life from the destruction an evil man seeks to perpetuate. Many places in scripture have a similar call to the defense and care of our neighbor or those that are weak. c.f Leviticus 19:15, Isaiah 1:17, & Proverbs 31:8-9
If you faint in the day of adversity, Your strength is small. Deliver those who are drawn toward death, And hold back those stumbling to the slaughter. If you say, “Surely we did not know this,” Does not He who weighs the hearts consider it? He who keeps your soul, does He not know it? And will He not render to each man according to his deeds?
It is a duty to assist or rescue the innocent when they are in danger by doing anything that is within our ability and in accordance with the rest of God's word. Commentary
But I tell you not to resist an evil person. But whoever slaps you on your right cheek, turn the other to him also.
This verse is not telling us that self-defense is unlawful or immoral. This verse speaks of a personal offense that falls short of a deadly threat. Deadly force is not to be used in the defense of life if a deadly threat is not present. It might be helpful to note, too, that those who wish to turn this verse into an argument for pacifism may not be willing to follow the next verse themselves. "And if any man will sue thee at the law, and take away thy coat, let him have thy cloak also." It is clear from the context that we aren't dealing with life-ending offenses. Commentary
But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you.
Because we recognize the image of God in man, because God has created man, we are called to love our enemies and not hate them or seek to harm them. Commentators point at that we are not to seek revenge but to bless those who hate us. This is not speaking to the defense of life from an imminent threat. An important principle of scriptural interpretation is that scripture interprets scripture, and that clear passages help us to rightly understand the less clear. When there are clear passages allowing the defense of life such as in Exodus 22:2-3, we should not then set a passage like this one against it. Commentary
John 18:10-11 (also Matthew 26:51-52)
Then Simon Peter, having a sword, drew it and struck the high priest’s servant, and cut off his right ear. The servant’s name was Malchus.
So Jesus said to Peter, “Put your sword into the sheath. Shall I not drink the cup which My Father has given Me?”
Matthew's version also states that those who live by the sword, die by the sword, which is taken by some as a renouncement of self-defense with tools that can be lethal. The context in these passages is that Jesus' task was to "drink the cup" that was before Him. When predicting His coming death in Matthew 16, to Peter's claim that he wouldn't allow it to happen, Jesus stated, “Get behind Me, Satan! You are an offense to Me, for you are not mindful of the things of God, but the things of men.” It wouldn't have been appropriate for Jesus to have been saved from this task.
Matthew's statement about living by the sword, and dies but is understood in different ways. Ir should first be remembered that as other passages make it clear that self-defense is permissible, this can't be understood to me that it is not. Barnes suggests that it could be a reference to those that came to take Jesus, that since they make use of the sword against the innocent, that they will die by it. Others speak about this as a prohibition against private revenge.
It should also be noticed that the disciples had swords in the first place. Jesus would not have been unaware that His disciples carried this tool for defense. Commentary
When a strong man, fully armed, guards his own palace, his goods are in peace.
Beloved, do not avenge yourselves, but rather give place to wrath; for it is written, "Vengeance is Mine, I will repay," says the Lord.
God has taught us that vengeance is His. Self-defense is NOT the pursuit of an enemy that is not immediately threatening our life. Vengeance like that belongs to God and He will use whatever means He determines, including the civil magistrate. We must not show a lack of faith in God's word to us that He will repay. Stopping an immediate threat is moral. Pursuing someone who is not an immediate threat and taking their life would be to become a murderer.