EXOD658 … the best and worthiest mercy of a father to his son is that which brings him to Divine service, as it is written (Yeshayahu 38:19): "A father will educate his sons to Your truth." He must pity his soul more than his body. And he must strike him with the rod of chastisement to guide him in the right path though it may seem cruel to do so, for such cruelty is mercy. And if one withholds the rod of chastisement from his son, his mercies having "kindled" against his striking him, and he allows him to follow the evil promptings of his heart, such a pity despoils him and deprives him of life in the World-to-Come. Similarly, even if one rears an orphan, concerning whom it is written [this verse]: "Do not affect any widow or orphan," it is a mitzvah to beat him to turn him to the right path. One must still treat an orphan more mercifully than others--but he must not allow him to do whatever he wishes. One must also not be too merciful with himself, but he must afflict himself and suppress his evil inclination.