However, even parents should not be excused for abandoning us, because they have preferred a younger son to an older one. At the same time, care must be taken that no one, while following their example, has an unfair judgment between their children; so that they think one should be loved, the other should be disregarded. For from this fraternal hatred is aroused, and a crime of parricide is made from the despicable gain of money. The same measure of piety should nourish offspring. Nevertheless, let it be that one may seize something more for himself in regard to a more charming or similar affection, an equal form of justice should be around all. It is more advantageous to the beloved one to whom the love of brothers is sought; but it is more taken away from the one who is burdened by unjust preeminence with envy. Esau was threatening to kill his brother, not being called back by brotherly kinship or the reverence of his parents from his murderous intent; and he was grieved that the blessing had been snatched away from him, which he must certainly prove himself worthy of by gentleness, not by wickedness.
Source: On Jacob and the Blessed Life