Question: "What does the Bible say about killing in war? Is killing in war a sin?"
Answer: There are many wars mentioned in the Bible. Wars of conquest (Joshua 1:6), civil wars (2 Samuel 3:1), and even a war in heaven (Revelation 12:7). Of course, wars involve killing; there is no way around it. We know that murder is sin (Exodus 20:13). But what about the killing of an enemy combatant during wartime?
First, we know that not all killing in wartime is a sin because there have been times when God Himself commanded battles to be fought. God told the ancient Israelites to possess the Promised Land; in fact, just before the conquest, the Lord appeared to Joshua as “commander of the army of the Lord”—a man of war (Joshua 5:14). God laid out the battle plans for the fight against Ai (Joshua 8:1–2). God told King Saul to “go, attack the Amalekites and totally destroy all that belongs to them” (1 Samuel 15:3). King David defeated the Philistines by following God’s strategy concerning the battle (2 Samuel 5:23–25). God never tells people to sin, so the Israelites who followed God’s commands to wage war were not sinning. Killing in war cannot be equated with murder.
This is not to say that killing in war has no effects. David wanted badly to build the temple in Jerusalem, but God did not let him. The Lord wanted a man of peace to build the temple, and David’s history had been anything but peaceful. God said to David, “You are not to build a house for my Name, because you are a warrior and have shed blood” (1 Chronicles 28:3).
There is no theocracy today. No nation has a command from God to wage war, and God is not handing out battle plans as He did to Joshua, Saul, and David. Yet wars continue to be fought. It is part of a fallen world’s existence. The Bible never condemns the actions of a soldier following orders on a battlefield. In fact, the New Testament has examples of soldiers who had faith in God—Jesus commended a centurion’s faith in Matthew 8:10; and another centurion, Cornelius, was saved in Acts 10. These men of war were not rebuked for performing the duties of a centurion, nor were they told they must change professions.
Most tellingly, some soldiers came to John the Baptist as he was baptizing in the Jordan River. The soldiers asked John, “What should we do?” This would have been the perfect opportunity for John to tell them to stop engaging in warfare, stop killing, or stop being soldiers. Instead, John replied, “Don’t extort money and don’t accuse people falsely—be content with your pay” (Luke 3:14). Being a soldier is not inherently sinful.
Paul uses the soldier life as an illustration of spiritual truth (see 1 Corinthians 9:7 and 2 Timothy 2:3). Other references mention battles and warfare (see 2 Corinthians 10:4 and 1 Timothy 1:18). Ephesians 6 contains an extended comparison of the Christian life and warfare (verses 10–17). If being a soldier (and doing the things soldiers are required to do) were sinful, it is unlikely the Holy Spirit would have used soldiering as a metaphor for anything good.
Throughout the Bible, warfare is presented as a grim reality in a cursed world. There are forces of evil that must be stopped, and bloodshed is sometimes the result. Whether a Christian should serve in the military is a matter of one’s own conscience, but killing an armed combatant in the context of warfare is not sinful in itself. There is a time and season for everything, including war (Ecclesiastes 3:8).