As Christians we strive to obey the Ten Commandments, including the command not to murder (Exodus 20:13; Matthew 19:18). We are also to love our neighbours as ourselves, and believe every human being is made in the image of God (Luke 10:25-37).
Romans 13:10 tells us: "Love does no harm to a neighbour; therefore love is the fulfillment of the law." Since love does no harm to a neighbour, how can a Christian be a part of a military organization that kills people?
Jesus never took a human life or acted violently toward another human being, and when threatened with violence, He avoided confrontation (Luke 4:28-30; John 8:59). Among Jesus' 12 disciples the only two violent incidents that occurred were condemned by Him, and the first was only a threat. James and John wanted to call fire from heaven to destroy a Samaritan village where they had been refused lodging (Luke 9:51-56). Jesus scolded them, "You do not know what manner of spirit you are of. For the Son of Man did not come to destroy men's lives but to save them."
The other case of violence occurred when Peter cut off the ear of a servant of the high priest as Jesus was being arrested. Jesus healed the ear and then rebuked Peter, "Put your sword in its place, for all who take the sword will perish by the sword" (Matthew 26:51-53).
The primary motivation and driving spiritual force of those called by God at this time is to "...seek first the kingdom of God and His righteousness..." (Matthew 6:33), as "ambassadors for Christ," (2 Corinthians 5:20). Our supreme, spiritual allegiance is to God and His Kingdom—not to any physical nation.
We are not of this world (John 17:14, 16). Jesus explained this to Pontius Pilate, "...My kingdom is not of this world. If My kingdom were of this world, My servants would fight..." (John 18:36). This is a key scripture showing Christians do not fight, are not violent and do not serve in the militaries of this world.
Romans 13:1-7 tells us a Christian should be subject to the governing powers of his nation, but a line must be drawn if the government orders you to do what is against the law of God, and kill others in a war. We must obey God first, even if it means suffering consequences (Acts 5:29).
But what about ancient Israel and why did David fight, when he was called a man after God's own heart? Ancient Israel was governed by God’s civil code, but most of her people were not spiritually converted and chose to fight, rather than trust God. Israel didn't have to go to war. God had promised to fight her battles, if the Israelites would have turned to Him and trusted Him (Exodus 14:14; Deuteronomy 1:30-32). God did execute certain judgments upon sinful nations through Israel, but God was not pleased David chose to be a man of war, and did not allow him to build the temple because of it (1 Chronicles 28:3).
Then there’s Cornelius, a centurion or noncommissioned officer in the Roman army. Some claim his example shows Christians can and should fight for their nation. He was the first gentile to be baptized in the New Testament (Acts 10:1-8, 44-48), and he and his household were in the process of learning "what manner of spirit" they were to live by -- a life not of war and military service, but of peace and obedience to God. Also, since his whole household was with him in Caesarea, he may have already retired from the Roman army.
In a speech in April, 1961, a priest and dean of Catholic University in Washington, D.C., summarised a long-standing, but erroneous, approach to the issue of Christians serving in the military: "A soldier may kill in time of war, but for him to kill in a spirit of hatred is not the proper Christian attitude." The Bible tells us not just to avoid hating, but not to kill at all: "...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, that you may be sons of your Father in heaven..." (Matthew 5:44-45).
Christians should not disregard the great sacrifice of those who gave their lives to defend their country. Their dedication is profound, and they acted on what they understood, but dedicated Christians have a different kind of battle to fight. Our weapons are spiritual (2 Corinthians 10:3-5), and when Jesus Christ returns to this earth we will have a part in bringing true peace to this earth.