We must love our enemies because Christ first loved us and did so for us. By the sin of our first parents, humans were separated from God. While it didn’t make us “enemies of God” in the sense that we think of human enemies, it did put us in a position that was only reconcilable by God himself. He who had been mortally sinned against first had to bridge that gap we could not bridge ourselves and reconcile us to himself. As he did, so must we do. We must seek reconciliation, to the extent that is possible, even with those who seem to be in an irreconcilable position from us.
As for the devil, because of his angelic nature, he cannot be reconciled with God. Humans, during their lifetimes, are still capable of reconciliation with God and neighbor.
