Why (was this)? Because he loved peace and pursued peace, and passed daily through the entire camp of Israel and promoted peace between a man and his wife, and between a man and his neighbour; therefore all Israel showed loving-kindness to him, as it is said, "And when all the congregation saw that Aaron was dead, they wept for Aaron thirty days, even all the house of Israel" (Num. 20:29).
Rabbi José said: From whom do we learn of the seven days of mourning? From Jacob, our father, for thus did his son Joseph unto him, as it is said, "And he made a mourning for his father seven days" (Gen. 50:10).