Leviticus 18:1

“And the Lord spake unto Moses, etc.] He continued speaking to him, after he had delivered to him the laws respecting the day of atonement, and the bringing of the sacrifices to the door of the tabernacle, and particularly concerning the Israelites not worshipping devils, as they had done in Egypt: the Lord proceeds to deliver out others, the more effectually to guard against both the immoral and idolatrous practice, of the Egyptians and Canaanites: saying, as follows.”

“UNLAWFUL MARRIAGES. (Lev. 18:1-30) I am the Lord your God--This renewed mention of the divine sovereignty over the Israelites was intended to bear particularly on some laws that were widely different from the social customs that obtained both in Egypt and Canaan; for the enormities, which the laws enumerated in this chapter were intended to put down, were freely practised or publicly sanctioned in both of those countries; and, indeed, the extermination of the ancient Canaanites is described as owing to the abominations with which they had polluted the land.”

“18:1–20:27 Chapters 18 and 20 primarily discuss sexual matters, warning against engaging in pagan practices both religious and secular. These chapters bracket exhortations to pursue holiness in everyday life (ch 19).”

“Holiness of the Marriage Relation. - The prohibition of incest and similar sensual abominations is introduced with a general warning as to the licentious customs of the Egyptians and Canaanites, and an exhortation to walk in the judgments and ordinances of Jehovah ( Lev 18:2-5), and is brought to a close with a threatening allusion to the consequences of all such defilements ( Lev 18:24-30). Lev 18:1-4 By the words, "I am Jehovah your God," which are placed at the head and repeated at the close ( Lev 18:30), the observance of the command is enforced upon the people as a covenant obligation, and urged upon them most strongly by the promise, that through the observance of the ordinances and…”