John Stackhouse explains what you need to believe in order to obey Jesus’ command.
The teaching to love your enemies is not just radical, it seems simply contradictory. I mean an enemy, by definition, is somebody who is out to get me, who is in my way and is trying to impede whatever good I’m trying to do, or achieve, or gain in the world. So to love somebody who’s against me sounds simply contradictory. It sounds counterproductive. Why would I do that? What possible good would that do for me, or for my kind, or for my cause? And what it does is to remind us that God is over all, that God is in every process, and that he can be trusted to work things out for good at a level that we can’t. And so we really do have to trust him that he’s going to work things out anyway, if I’m going to follow this apparently preposterous idea that I should love my enemy.