It was the teaching position of the early church that Christians should not kill others, even in time of war, since we are called to love our enemies. The following quotes illustrate this.
Justin Martyr (150’s) – “. . . We who hated and destroyed one another, and on account of their different manners would not live with men of a different tribe, now, since the coming of Christ, live familiarly with them, and pray for our enemies, and endeavor to persuade those who hate us unjustly to live conformably to the good precepts of Christ, to the end that they may become partakers with us of the same joyful hope of a reward from God the ruler of all.” Apology 14; “And of our love to all, He taught thus: ‘If ye love them that love you, what new thing do ye? For even fornicators do this. But I say unto you, pray for your enemies, and love them that hate you, and bless them that curse you, and pray for them that despitefully use you.’” Apology 15; “We who formerly used to murder one another do not only now refrain from making war upon our enemies, but also, that we may not lie nor deceive our examiners, willingly die confessing Christ.” First Apology 39; “We who were filled with war and mutual slaughter and every wickedness have each of us in all the world changed our weapons of war . . . swords into plows and spears into agricultural implements” (referring to Micah 4:1-4; Isaiah 2:2-4). Dialogue with Trypho 110.
Athenagoras (176-177) “We cannot endure even to see a man put to death, though justly . . ..” Plea for Christians 35.
[Celsus (178) – a pagan critic of Christianity acknowledged the early church’s position that Christians should not kill others, including in war.]
Irenaeus (175-185) Speaks of Christians as those who “did form the swords and war-lances into ploughshares, and changed them into pruning-hooks for the reaping of corn, that is, into instruments for peaceful purposes, and that they are now unaccustomed to fighting, but when smitten, offer also the other check . . ..” Against Heresies 4, 34, 4.
Tertullian (late 100s’s early 200’s) wrote extensively on this topic. “If we are ordered, as we said above, to love our enemies, whom have we left to hate? Likewise, if when injured we are forbidden to retaliate, lest by our action we should put ourselves on the level of our enemy, whom can we injure?” Apology 37; In Christianity it is “counted better to be slain, than to slay.” Apology 42, 2; “There can be no compatibility between the divine and the human sacrament [the military oath], the standard of Christ and the standard of the devil, the camp of light and the camp of darkness. . . But how will a Christian man go to war? Indeed how will he serve in peacetime without a sword which the Lord has taken away? . . The Lord in . . . disarming Peter disarmed every soldier.” On Idolatry 19; “Shall it be held lawful to make an occupation of the sword, when the Lord proclaims that he who uses the sword shall perish by the sword? And shall the son of peace take part in the battle when it does not become him even to sue at law?” On the Military Crown 11.
Hippolytus – (215) “A soldier who is in authority must be told not to execute men; if he should be ordered to do it, he shall not do it.” The Apostolic Tradition 16, 17.
Clement of Alexandria (Early 200’s) – “For it is not in war, but in peace, that we are trained.” The Instructor 1, 12; “For we do not train our women . . . in war; since we wish the men even to be peaceable.” Stromata 4, 8; “The loud trumpet, when sounded, collects the soldiers, and proclaims war. And shall not Christ, breathing a strain of peace to the ends of the earth, gather together his own soldiers of peace? Well, by his blood, and by the word he has gathered the bloodless host of peace, and assigned to them the kingdom of heaven.” Exhortation 11, 116.
Origen (248) – “God did not deem it becoming to his own divine legislation to allow the killing of any man whatever.” Against Celsus 3, 7; “And to those who inquire of us whence we come, or who is our founder, we reply that we are come, agreeably to the counsels of Jesus, to ‘cut down our hostile and insolent ‘wordy’ swords into ploughshares, and to convert into pruning-hooks the spears formerly employed in war.’ For we no longer take up ‘sword against nation,’ nor do we ‘learn war any more,’ having become children of peace, for the sake of Jesus . . ..” Against Celsus 5, 33; “We do not fight under the Emperor, although he require it.” Against Celsus 8, 73.
Cyprian (mid 200’s) “Observe the roads blocked by robbers, the seas beset by pirates, wars spread everywhere with the bloody horrors of camps. The world is soaked with mutual blood, and when individuals commit homicide, it is a crime; it is called a virtue when it is done in the name of the state.” To Donatus 6.
Lactantius – (304-305) “For when God forbids us to kill, He not only prohibits us from open violence, which is not even allowed by the public laws, but He warns us against the commission of those things which are esteemed lawful among men. Thus it will be neither lawful for a just man to engage in warfare, since his warfare is justice itself, nor to accuse any one of a capital charge, because it makes no difference whether you put a man to death by word, or rather by the sword, since it is the act of putting to death itself which is prohibited.” Divine Institutions 6, 20.
Arnobius (304-310) “. . . it would not be difficult to prove, that after the name of Christ was heard in the world, not only were (wars) not increased, but they were even in great measure diminished by the restraining of furious passions. For since we, a numerous band of men as we are, have learned from His teaching and His laws that evil ought not to be requited with evil, that it is better to suffer wrong than to inflict it, that we should rather shed our own blood than stain our hands and our conscience with that of another, an ungrateful world is now for a long period enjoying a benefit from Christ, inasmuch as by His means the rage of savage ferocity has been softened, and has begun to withhold hostile hands from the blood of a fellow-creature.” Against the Nations 1, 6.
Through the first two and half centuries after the apostles, the church was clear in its teaching that Christians should not kill, even in war. Some who served in the military, upon becoming Christians would quit the army. Some were persecuted and killed for confessing Jesus in the military. Others were killed for refusing to join based on their Christian faith.
This all changed as time went on. Christianity became more socially acceptable and more Christians voluntarily joined the army. This was especially the case after Constantine, the Roman emperor, converted to Christianity in 310. Christianity became the official religion of the Empire in 380. By the early 400’s you had to be a Christian to be in the military.
