City of God

But the character of the human will is of moment; because, if it is wrong, these motions of the soul will be wrong, but if it is right, they will be not merely blameless, but even praiseworthy. For the will is in them all; yea, none of them is anything else than will. For what are desire and joy but a volition of consent to the things we wish? And what are fear and sadness but a volition of aversion from the things which we do not wish? But when consent takes the form of seeking to possess the things we wish, this is called desire; and when consent takes the form of enjoying the things we wish, this is called joy.

In like manner, when we turn with aversion from that which we do not wish to happen, this volition is termed fear; and when we turn away from that which has happened against our will, this act of will is called sorrow. And generally in respect of all that we seek or shun, as a man's will is attracted or repelled, so it is changed and turned into these different affections. Wherefore the man who lives according to God, and not according to man, ought to be a lover of good, and therefore a hater of evil.

And since no one is evil by nature, but whoever is evil is evil by vice, he who lives according to God ought to cherish towards evil men a perfect hatred, so that he shall neither hate the man because of his vice, nor love the vice because of the man, but hate the vice and love the man. For the vice being cursed, all that ought to be loved, and nothing that ought to be hated, will remain.