And Esau hated Jacob because of the blessing with which his father blessed him: and Esau said in his heart, The days of mourning for my father are at hand; then will I slay my brother Jacob.
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Ambrose of Milan
But we shouldn’t leave his parents without excuse for having preferred their younger son to the elder. At the same time we must take care so that no one, in turning to their example, would make an unfair judgment between his sons or suppose that he should love the one and esteem the other less. From this line of conduct fraternal hatreds are aroused and the crime of fratricide is contrived to gain a worthless sum of money. Let children be nurtured with an equal measure of devotion. Granted that one’s love may fasten more upon some trait in a child who is more agreeable or similar to oneself, the exercise of justice ought to be the same in regard to all. The more that is given to the child that is loved and who seeks his brother’s love, the more is taken away from the one who is burdened with jealousy at the unfair preferment. Esau threatened that he would kill his brother. Neither the fact of brotherhood nor respect for their parents kept him from his fratricidal madness, and he grieve...
My father. He has no regard for this mother. (Menochius)
Her love for Jacob filled him with greater indignation; and he resolved to murder him, in order, perhaps, to revenge himself on both. Though this cruel resolution was taken in his heart, with full deliberation, he was not so careful to conceal his intentions; but his watchful mother discovered it, and by her prudence, preserved him from committing the external sin: and Jacob from falling a prey to this second Cain.