I know what you’re thinking: “Doesn’t the New Testament say things like, ‘Love your enemy,’ ‘Turn the other cheek,’ etc.?” You are right, the New Testament does make those statements, and many others similar; however, those statements are all addressed to the individual, many in the context of dealing with persecution. Not one of those statements is addressed to a nation, or monarch as monarch, or a magistrate as magistrate.
Indeed, the king or magistrate must do everything in his power to protect those under his care and to preserve their dignity and liberty as human beings. Allowing another nation to overtake and oppress your people out of a misguided sense of love certainly will not accomplish that. The sad truth is that we live in a fallen world, and violence is sometimes necessary to quell violence and to prevent greater violence. Many of us don’t have it in us to chase down bad guys, but when we are in need, we are thankful that there are those who not only have it in them to do such things, but we are grateful that they are willing to do what is necessary to restrain the lawbreaker. What good is a law if the law is not enforced or unenforceable?
Some say that there are no passages that permit the Christian personally to participate in warfare (serving as a soldier) or violence of any kind (serving as a policeman, or defending oneself), even if the individual or nation is engaged in a worthy struggle. (Calvin addressed this same question in his Institutes, Book IV, Ch. Xx., Sec. 11 and I rely somewhat on him in this argument. His Institutes may be found online here. If I remember correctly, and I cannot cite a source, but it seems that even Luther believed that “The sword belongs to the magistrate,” and so believed that individuals were not permitted to use violence, even in defense of their own person.) While it is true that one should not tend toward violence nor should one use violence hastily or in any other way than as a last resort, the fact is that nowhere in the Bible is a Christian expressly forbidden to defend himself, except when facing persecution, nor to participate in a war in defense of his nation or people.
It is telling that in the New Testament, when soldiers seek salvation, they are not told to lay down their arms to be saved, they are simply told, “Do not intimidate anyone or accuse falsely, and be content with your wages.” (Luke 3:14). The Scriptures, both Old and New Testament, assume that the authorities will enforce the law and that nations will defend themselves and there is understanding that violence is sometimes necessary in such endeavors. Magistrates, by which I mean those committed to enforcing laws and protecting the citizenry, must be careful not to use violence needlessly or unjustly, but if they fail to defend those who are under their care and charge, they have not discharged their duties faithfully and have failed those who have chosen them to serve.
So those who choose to be pacifist are certainly free to choose that way of life and to believe in it as the ideal, although, as long as we live in a fallen world, that seems more than a little unrealistic to me. Pacifists, however, must look to somewhere other than the Scriptures in order to justify their position.