Ecclesiastes says there is both a time for war and a time to kill. (Ecclesiastes 3:1-8) The fifth commandment, “Thou shalt not kill” seems to contradict God’s commands for war and killing. (Exodus 20:13) But when Moses explains this command, we see that God is talking about an unjust, intentional killing. (Numbers 35:11 / Joshua 20:9) In fact the penalty for disobeying the commandment not to kill, is to be killed. (Exodus 21:12)

Some might argue that the New Testament replaces the Old Testament. But the book of Hebrews clarifies that the new testament only did away with the old covenant (namely, being perfect by obeying all the laws of Moses and circumcision (John 7:19-22 / Galatians 5:2-6 / James 2:10 / Matthew 19:16-19)). (Hebrews 8:7-13 / Romans 7:1-6)All other parts of the Old Testament are still quoted as authoritative by Jesus and his Apostles, in the New Testament. (Matthew 5:17-18 / Old Testament quotes in the New Testament)

The government is given the authority to bear the sword, by God, and we are commanded to obey them, if they are in line with God’s will. (Romans 13:4 / Romans 13:1 / Romans 12:18) If it’s God’s will to go to war or kill, it would be a sin to refuse. (1 Kings 20:42 / Romans 13:2)

Knowing if a war is God’s will can be tricky, because Satan disguises himself as an angel of light, and he influences the government. (2 Corinthians 11:14 / Ephesians 6:12) We are told to learn God’s will by studying and applying the bible, and through prayer, so we know what God wants us to do. (Hebrews 5:14 / Ephesians 5:17 / Psalm 119:11 / James 1:5) We are also told to pray for the authorities, so God will use them to restrain evil and not cause it. (1 Timothy 2:1-2 / 2 Thessalonians 2:6-7) God appoints all authorities, even corrupt ones, such as Rehoboam, Nebuchadnezzar, or Pilot, who crucified Jesus. (1 Kings 12:21-24 / Jeremiah 27:6 / John 19:10-11 / Isaiah 45:1) “The king’s heart is in the hand of the Lord like channels of water; he turns it wherever he wishes.” (Proverbs 21:1) So, it’s up to God whether we have peace or persecution, and whether we should fight for our authorities or not.