Nigel Biggar offers three reasons for the early church’s rejection of war and violence.
The grounds for Christian pacifism are very plain. In the Gospels, Jesus enjoins his disciples to love, to love their enemy, to forgive, when struck upon one cheek to offer another cheek. So there is clearly a very strong pacific element in the Gospels. And even in the Epistles of St Paul – Paul talks about not retaliating and forgiving as well. So there’s certainly scriptural grounds that pacifists ground their position on.
Next, in the history of the early church, the context was the Roman Empire and Christians found Roman culture often to be quite bloodthirsty, so you’ll have … we have extant Christian writings against the Roman circuses, about the bloodshed. We in the West nowadays, we throughout the world, we love to watch gory movies. Well, the Romans went one further. They watched the real thing. They watched human beings being slaughtered by other human beings or by animals. And they thought it was fun. And Christians found it disgusting. And oftentimes Christians would associate bloodthirsty Roman culture with the Roman military.
And then the third reason that pacifism got off the ground was the fact that for the first 300 years or so, Christians did not occupy public office. They didn’t have the responsibility of maintaining public order, which throughout history has required the use of force. So those are the reasons that Christian pacifism took off.