In preparing for Sunday I came across this commentary remark that I find helpful and fascinating.
Matthew 5.43-45 in the Williams translation reads: You have heard it said, 'you must love your neighbor and hate your enemy.' But I tell you, practice loving your enemies and praying for your persecutors to prove that you are the sons of your Father in heaven, for He makes His sun to rise on bad as well as good people, and makes the rain come down on does of right and wrong alike.
Here's a commentary found in the Ancient Christian Commentary on Scripture:
The hatred of an enemy is destroyed by the love of friendship. Suppose you have viewed a man as an enemy, yet after a while he has been swayed by your benevolence. You will then love him as a friend. I think that Christ ordered these things not so much for our enemies as for us: not because enemies are fit to be loved by others but because we are not fit to hate anyone. for hatred is the prodigy of dark places. Where it resides, it sullies the beauty of sound sense. Therefore not only does Christ order us to love our enemies for the sake of cherishing them but also for the sake of driving away from ourselves what is bad for us.
The Mosaic law does not speak about physically hurting your enemy but about hating your enemy. But if you merely hate him, you have hurt yourself more in the spirit than you have hurt him in the flesh. Perhaps you don't harm him at all by hating him. But you surely tear yourself apart. If then you are benevolent to an enemy, you have rather spared yourself than him. And if you do him a kindness, you benefit yourself more than him." (from Incomplete Work on Matthew, Homily 13)