Kabbalah zu Bereschit 25:22

Rabbi Yitzchak said, It is written, "And the children struggled together within her; and she said, 'if it be so, why am I thus?' And she went to inquire of Hashem" (Gen. 25:22). Where did she go? To the academy of Shem and Ever. "the children struggled together within her," because the wicked Esau was warring against Jacob there. The term 'struggle' (Heb. וַיִּתְרֹצֲצוּ) is similar to the expression 'to break' (Heb. רָצַץ) one's head, for they struggled and were divided. Come and behold, Esau was of the side of he who rides the serpent, (Samael) while JACOB was of the side who rides the perfect Holy Throne, of the side of the sun, that is united with the moon.