"... Although the rest of the Torah would not be intelligible without the background provided in the Book of Genesis, this work nevertheless constitutes a distinct and discrete unit within that literary corpus. Its individuality and antiquity are asserted in numerous ways ... Abraham married his half-sister, an act that is repeatedly forbidden in the law collections. Jacob was simultaneously married to two sisters, mothers of the tribes of Israel, a marriage arrangement that is outlawed in Leviticus 18:18. Judah and Tamar understand that the levirate obligation extends even to the father of the deceased, childless husband; but according to Deuteronomy 25:5–10, it is restricted to the brothers. Indeed, the offspring of the union of Judah and Tamar—which would later be considered an illicit union—becomes the ancestor of the royal line of David. And whereas intermarriage with foreigners, natives of Canaan, is prohibited in Exodus 34:16 and Deuteronomy 7:3, no such interdiction is either assumed or implied in the narratives of Genesis. Simeon and Levi voice no religious objection to the proposal of the Shechemites to intermarry with Jacob’s family. Their sole concern is the violation of their sister. Both Judah and Simeon married Canaanite women; and Joseph took to wife the daughter of an Egyptian priest, a union that produces two of the tribes of Israel. In general, religious differences between the patriarchs and foreigners are never a source of tension. The only sins attributed to non-Israelites are of the moral kind; idolatry, a major theme in the rest of the Bible, is never mentioned ..."

Sarna, Nahum M Genesis: The Traditional Hebrew Text with New JPS Translation (p. xv) Jewish Publication Society, 1989