Variantly: "And he said: The L-rd came from Sinai.": When the L-rd is destined to exact payment of Seir, He is destined to "thunder" all of the world on its inhabitants, as He did at the giving of the Torah, viz. (Judges 5:14) "O L-rd, when You went out of Seir, when You strode from the field of Edom, the earth thundered; the heavens, too, trickled; the heights, too, dripped water."
Variantly: To what may this be compared? To one who desired to give a gift to one of his sons, but feared his brothers, his lovers, and his kinsmen. What did that son do? He arose and exposed himself and shore his hair, whereupon the king said to him: To you shall I give the gift. Similarly, when our father Abraham came to the world, a blemish issued from him — Yishmael and the sons of Keturah reverted to wickedness, more than their predecessors. When Isaac came, a blemish issued from him — Esav and all the chiefs of Edom. But in Jacob no blemish was found, as it is written (Bereshith 25:27) "And Jacob was an upright man, a dweller of tents" — whereupon the L-rd said to him: To you shall I give the Torah — wherefore it is written "And he said: The L-rd came from Sinai, etc."