Many texts in the New Testament seem to be strongly pacifist in nature — for example, "turn the other cheek" and "love your enemies" from Christ's Sermon on the Mount, Jesus' command to Peter to "put away the sword," St. John the Baptist's admonition to soldiers to "do no violence," and so on.
While it is true that a number of passages may seem to be pacifist in nature, the question relevant to Christian societies and individual believers faced with the decision to confront evildoers is whether or not the New Testament morally assesses the war-fighting profession. It does not. Let us first look at some examples of military figures and imagery in the New Testament.
In Luke 14:31-33 the Lord Himself, in explaining the costs of discipleship, invokes the image of a king considering war with ten thousand troops against another king with twenty thousand troops. It stands to reason that if our Lord categorically disapproved of all war and violence on spiritual and/or moral grounds, He would not have used war between kings to illustrate the costs of discipleship.
St. John the Baptist tells soldiers to be content with their wages and "do violence to no man." If St. John disapproved of all war and violence, why would he tell soldiers merely to be content with their wages? He would have exhorted them to abandon the war-fighting profession altogether. But "do violence to no man" cannot mean "do not kill" otherwise the soldiers cannot be soldiers; they would immediately have had to give up their profession. Other translations have this phrase as "rob no man by violence" and this, rather than "do violence to no man," seems to be closer to the original intent: rather than prohibiting warfare in general, the Baptist is saying that soldiers are not to loot or commit other crimes during war.
Military figures abound in the New Testament. The Roman soldiers who mocked Jesus are depicted as evil for so they were. The Roman Centurion whose faith was pronounced by Christ Himself to be greater than any found in Israel is depicted as good and noble. Some military figures, like Pontius Pilate, stand conflicted, wanting to do good, trying to wash their hands of evil, but in the end, succumbing to evil. Each vignette speaks to the individual, personal characters of the soldiers in question; it does not render a moral assessment of war and of the war-fighting profession.
St. Paul also employs military imagery in speaking about the armor of God: the breastplate of righteousness, the sword of the spirit, the helmet of salvation, and so forth. In 1 Timothy 1:18, St. Paul exhorts Timothy to "wage a good warfare." It is unlikely that had St. Paul categorically disapproved of the war-fighting profession, he would have used military imagery to illustrate spiritual truths.
Is Christ's command to Peter to put away his sword in John 18:10-11 an injunction against war? In these difficult passages, context is key to understanding. Judas Iscariot had just betrayed the Lord, and Jesus was about to be hauled off to His trial, crucifixion, and death. To understand Christ's command, therefore, we must recall that there are many things that Christ did not do whilst He was present on earth — He did not become a tailor, take a wife, or become a politician. Some Jews wanted Him to be a warrior-king like David and deliver them from the oppression of the Romans. But it was not His task to do those things either.
The mission of Christ was to do the will of His Father: deliver His children from the spiritual chains of sin, death, and the devil, from which we could never deliver ourselves. Christ's was a heavenly commission, not an earthly one. He Himself explained to Pilate that He could call down twelve legions of angels, but how then would the Scriptures be fulfilled? Similarly, had His disciples physically defended Jesus, had Jesus not allowed Himself to be taken by the Sanhedrin, had His disciples been killed in scuffles with the temple guards, or had He not been put to death, how would His mission have been fulfilled? Thus He said to Peter, "put away your sword," not because Peter's sword was in and of itself evil, but because He was not going to allow Peter or anyone else stand in the way of accomplishing that mission: "the cup which my Father hath given me, shall I not drink it?" (John 18:10) — Scripture had to be fulfilled.
As we have seen, military persons and images are quite common throughout the New Testament. But nowhere in the New Testament do we see a moral assessment of the war-fighting profession on its own terms; notably, we do not see its condemnation.