John Calvin Commentary Leviticus 18:1

"And Jehovah spake unto Moses, saying," — Leviticus 18:1 (ASV)

And the Lord spoke to Moses. I have not introduced this declaration among other similar ones, which aimed at preparing their minds for the reverent reception of the Law. This is because, whatever similarity there may be in the words themselves, in their substance, there is a great difference; for those declarations were general, while this one is specifically limited to a single point.

For it was not God’s intention here merely to urge the people to study the Law. Instead, the instruction concerning the keeping of His statutes is directed to the current issue. He does not refer without distinction to all His own statutes and those of the Gentiles, but restricts Himself to the specific subject matter. Therefore, by “the statutes of the Gentiles,” He means those corruptions by which they had perverted His pure institution of holy matrimony.

First, however, He forbids them from following the customs of the Egyptians, and then He includes all the Canaanite nations. For, since all Eastern peoples are lustful, they never had any hesitation in defiling themselves with incestuous marriages. Indeed, history clearly shows how great the excesses of the Egyptians ⁸⁶ were in this respect.

A brother felt no abhorrence of marrying his sister from the same mother, nor did an uncle feel any about marrying his niece, whether on his father's or mother's side. In short, they were so dead to shame that they were overcome by their lusts, trampling on all the laws of nature. This is the reason God here lists the kinds of incest, the mention of which would otherwise have been unnecessary.

⁸⁶ “A very objectionable custom, which is not only noticed by Diodorus, but is fully authenticated by the sculptures both of Upper and Lower Egypt, existed among them from the earliest times, the origin and policy of which it is not easy to explain — the marriage of brother and sister, which Diodorus supposes to have been owing to, and sanctioned by, that of His and Osiris; but as this was purely an allegorical fable, and these ideal personages never lived on earth, his conjecture is of little weight; nor does any ancient writer offer a satisfactory explanation of so strange a custom.” — Wilkinson’s Popular Account of the Ancient Egyptians, 2:224.