Good timing on this topic. This touches on the topic for my class tomorrow which is about "Sanctity of Human Life". The background passages are Exodus 20:13; 21:22-25; 22:21-24, Deuteronomy 24:17-22; Matthew 5:21-26; and Luke 20:47.
The Biblical Truth we are studying is God has assigned the highest value to human life and calls for us to protect it.
However, knowing the men in my class, their character and make up, inevitably the question will be asked about self defense as well as what the Bible has to say about it.
Here are the verses and comments from John Gill I plan to use to answer those questions:
If a thief is found breaking in and is struck so that he dies, there shall be no bloodguilt for him, (Exodus 22:2 ESV)
Now there was no blacksmith to be found throughout all the land of Israel, for the Philistines said, "Lest the Hebrews make themselves swords or spears." But every one of the Israelites went down to the Philistines to sharpen his plowshare, his mattock, his axe, or his sickle, (1 Samuel 13:19-20 ESV)
And David said to his men, "Every man strap on his sword!" And every man of them strapped on his sword. David also strapped on his sword. And about four hundred men went up after David, while two hundred remained with the baggage. (1 Samuel 25:13 ESV)
Of David. Blessed be the LORD, my rock, who trains my hands for war, and my fingers for battle; (Psalms 144:1 ESV)
God is a man of war himself; and he teaches the art of war, as he does husbandry and other things; see Exo_15:3; and so the Lord furnishes his people, who are here in a militant state, with spiritual armour, to fight against their spiritual enemies; he teaches them how to put it on, and directs them how to make use of every piece of it; as well as gives them boldness to face their enemies, and victory over them. John Gill
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. (Luke 22:36 ESV)
Jesus words were mighty;
"Do not think that I have come to bring peace to the earth. I have not come to bring peace, but a sword. (Matthew 10:34 ESV)
By the "sword" may be meant the Gospel, which is the means of dividing and separating the people of Christ from the men of the world, and from their principles and practices, and one relation from another; as also of divisions, discords, and persecutions arising from it: not that it was the intention and design of Christ, in coming into the world, to foment and encourage such things; but this, through the malice and wickedness of men, was eventually the effect and consequence of his coming; see Luk_12:51 where, instead of a "sword", it is "division"; because the sword divides asunder, as does the sword of the Spirit, the word of God. John Gill
Those who carried burdens were loaded in such a way that each labored on the work with one hand and held his weapon with the other. And each of the builders had his sword strapped at his side while he built. The man who sounded the trumpet was beside me. (Nehemiah 4:17-18 ESV)
Beat your plowshares into swords, and your pruning hooks into spears; let the weak say, "I am a warrior." (Joel 3:10 ESV)
let the weak say, I am strong; such as are weak, through sickness, or old age, let them not plead their weakness to excuse them from engaging in this war; but let them make the best of themselves, and say they are strong and healthy, and fit for it, and enter in it with all courage and bravery: this is said either ironically to the enemies of God's people, suggesting that all hands would be wanted, and should be employed, weak and strong, and all little enough; when they had made the utmost effort they could, it would be in vain: or else they are seriously spoken to the people of God, that none of them should excuse themselves, or be discouraged because of their weakness from engaging in this last and more battle; but take heart, and be of good courage, and quit themselves like men, and be strong, since they might be sure of victory beforehand. The Apostle Paul refers to this text in 2Co_12:10; and applies it to spiritual weakness and strength; and indeed the weakest believer, that is so in faith and knowledge, may say he is strong, in comparison of what he once was, and others are; strong, not in himself, but in Christ, and the power of his might, and in the grace that is in him; nor should he excuse himself from fighting the Lord's battles, against sin, Satan, and the world, and false teachers; or from doing the Lord's work, any service he calls him to; or from bearing the cross he lays on him on account of his weakness; nor should he: be discouraged by it from those things; but let him strengthen himself, as Aben Ezra interprets it, take heart, and be of good courage. John Gill
Jesus clearly taught that we should never be retaliatory, or vengeful, (Matthew 5:38-39), but none the less, we are to be "wise as serpents and innocent as doves." We are to care and protect the weak, the widows, and the fatherless.