Keeping in mind that love does not refer here to an emotion, but an active will to the good of the other, Christian charity (caritas, love, aggape) becomes they most potent form of destroying one's enemies by making them enemies no more. This is in keeping with how Christ exceedingly fulfills the old Law in every way, and God's way is not our way.
Saint Hilary (c.315-367), Bishop of Poitiers, Doctor of the Church
On Matthew, IV, 27
“Be perfect as your heavenly Father is perfect”
“You have learnt what is said: Love your neighbor and hate your enemy…” In fact the Law required love of neighbor but allowed freedom to hate one’s enemy. Faith demands that we love our enemies. By means of a universal feeling of charity it breaks the movements of violence in man’s spirit, not just by restraining its vengeful anger but even more by pacifying it to the point of making us love those in the wrong. To love those who love you belongs to the pagan and we all have an affection for those who show it to us themselves. So Christ is calling us to live as children of God and imitate Him who, through the coming of his Christ, gives sun and rain to the good and the guilty alike in the sacraments of baptism and the Spirit. In this way he forms us according to the perfect life by means of this bond of kindness to all by calling us to imitate a heavenly Father who is perfect.