C. F. Keil and Franz Delitzsch on Genesis 25:22-23

Gen 25:22-23

When Rebekah conceived, the children struggled together in her womb. In this she saw an evil omen, that the pregnancy so long desired and entreated of Jehovah would bring misfortune, and that the fruit of her womb might not after all secure the blessing of the divine promise; so that in intense excitement she cried out, “If it be so, wherefore am I?” i.e., why am I alive? cf. Gen 27:46. But she sought counsel from God: she went to inquire of Jehovah. Where and how she looked for a divine revelation in the matter, is not recorded, and therefore cannot be determined with certainty. Some suppose that it was by prayer and sacrifice at a place dedicated to Jehovah. Others imagine that she applied to a prophet - to Abraham, Melchizedek, or Shem (Luther); a frequent custom in Israel afterwards (1Sa 9:9), but not probable in the patriarchal age. The divine answer, couched in the form of a prophetic oracle, assured her that she carried two nations in her womb, one stronger than the other; and that the greater (elder or first-born) should serve the less (younger). הפּרד ממּעיך: “proceeding from thy womb, are separated.”