Early in the Old Testament, war was frequently viewed as a holy war, a conflict started and guided by God. God Himself declared such a war (Exodus 17:16; Numbers 31:1-3, 1 Samuel 15:1-3), and every aspect of the conflict had religious importance. To secure God's continuous support, sacrificial ceremonies were performed (1 Samuel 7:8-10; 13:9). The precious ark of the covenant, which symbolised God's presence, was frequently carried into war (1 Samuel 4:3).

—The law will go out from Zion, the word of the LORD from Jerusalem. He will judge between the nations and will settle disputes for many peoples. They will beat their swords into plowshares and their spears into pruning hooks. Nation will not take up sword against nation, nor will they train for war anymore. (NIV, Isaiah 2:3-4)

War is universally viewed as evil in the New Testament, and Jesus advocated peace instead. He counselled us to eschew vengeance and retaliation, and to love even our adversaries.

—Never pay back evil for evil to anyone. Respect what is right in the sight of all men. If possible, so far as it depends on you, be at peace with all men. Never take your own revenge, beloved, but leave room for the wrath of God, for it is written, "Vengeance is Mine, I will repay," says the Lord. "But if your enemy is hungry, feed him, and if he is thirsty, give him a drink; for in so doing you will heap burning coals upon his head." Do not be overcome by evil, but overcome evil with good. (NAS, Romans 12:17-21)