Sunday Sermonette: It's complicated

Yes, this is more complicated than it might appear. Incest taboos are pretty much a universal in human culture, with or without specific religious proscription. Incest is against civil law in all modern societies, although standards do vary about cousins. As far as I can tell sexual relations between cousins are not forbidden here. Since the Israelites are polygamous, however, some of these additional instructions are needed, and they're probably a very good idea to prevent jealousy and family violence. However, the real point of much of Leviticus 18 is to slander the other inhabitants of Canaan and justify the Israelites' expropriation of their land. It is quite unlikely that they tolerated incest in fact. Same with the Egyptians but they are mentioned only for the sake of the fictitious setting in which this takes place. I'll talk about Molech when we get there. Note that with a couple of exceptions, this is addressed to men. They are assumed to have agency in sex.

18 And the Lord said to Moses, ² “Say to the people of Israel, I am the Lord your God. ³ You shall not do as they do in the land of Egypt, where you dwelt, and you shall not do as they do in the land of Canaan, to which I am bringing you. You shall not walk in their statutes. ⁴ You shall do my ordinances and keep my statutes and walk in them. I am the Lord your God. ⁵ You shall therefore keep my statutes and my ordinances, by doing which a man shall live: I am the Lord.

⁶ “None of you shall approach any one near of kin to him to uncover nakedness. I am the Lord. ⁷ You shall not uncover the nakedness of your father, which is the nakedness of your mother; she is your mother, you shall not uncover her nakedness. ⁸ You shall not uncover the nakedness of your father’s wife; it is your father’s nakedness. ⁹ 

Note that "your father's wife" in this context is not your mother, who has already been named. This refers to your father's other wives. "It is your father's nakedness" probably means that she is your father's sexual possession, not that having sex with her would be equivalent to having sex with your father. The euphemism here makes this a bit hard to interpret, but I'm pretty sure that's the idea.

You shall not uncover the nakedness of your sister, the daughter of your father or the daughter of your mother, whether born at home or born abroad. ¹⁰ 

Again, this presumably means half sister. Note, however, that Abraham married his half sister. 

You shall not uncover the nakedness of your son’s daughter or of your daughter’s daughter, for their nakedness is your own nakedness. ¹¹ You shall not uncover the nakedness of your father’s wife’s daughter, begotten by your father, since she is your sister. ¹² You shall not uncover the nakedness of your father’s sister; she is your father’s near kinswoman. ¹³ You shall not uncover the nakedness of your mother’s sister, for she is your mother’s near kinswoman. ¹⁴ You shall not uncover the nakedness of your father’s brother, that is, you shall not approach his wife; she is your aunt. ¹⁵ 

Since seems to make it more clear that "the nakedness of your father's brother" means his sexual possession, i.e. your aunt. Homosexuality is dealt with separately below.

You shall not uncover the nakedness of your daughter-in-law; she is your son’s wife, you shall not uncover her nakedness. ¹⁶ You shall not uncover the nakedness of your brother’s wife; she is your brother’s nakedness. ¹⁷ You shall not uncover the nakedness of a woman and of her daughter, and you shall not take her son’s daughter or her daughter’s daughter to uncover her nakedness; they are your^[a] near kinswomen; it is wickedness. ¹⁸ And you shall not take a woman as a rival wife to her sister, uncovering her nakedness while her sister is yet alive.

Note that this does not say that a man cannot have sex with his daughter. Maybe it's just an oversight. Nor are first cousins off limits.

¹⁹ “You shall not approach a woman to uncover her nakedness while she is in her menstrual uncleanness. ²⁰ And you shall not lie carnally with your neighbor’s wife, and defile yourself with her. ²¹ 

Although adultery is here defined as a sin committed by the man, we shall see later that women get the worst of it.

You shall not give any of your children to devote them by fire to Molech, and so profane the name of your God: I am the Lord. ²² 

For centuries, people read this as referring to a purported Canaanite God named Moloch, to whom children were sacrificed. Modern scholars doubt this, however. In the first place, as we have mentioned Biblical Hebrew lacks vowels. MLK, which is transliterated here as Moloch, usually means malek, "king." There is no evidence anywhere outside of the Hebrew Bible for a Canaanite God called Moloch; nor is there evidence that human sacrifice of any kind, let alone child sacrifice, was practiced in Canaan. There are a few possibilities here. One is that this is another slander against the Canaanites. Another is that "devote them by fire" refers to a purification ritual, not actually burning them, which actually seems very likely. And that leaves the additional possibility that MLK is not a God at all, but that this is rather some sort of civil ceremony; or that MLK is in fact Yahweh, and this is forbidding a particular ritual, not the worship of another God. Some scholars believe that MLK and YWH are the same entity.

You shall not lie with a male as with a woman; it is an abomination. ²³ And you shall not lie with any beast and defile yourself with it, neither shall any woman give herself to a beast to lie with it: it is perversion.²⁴ 

Note that lesbianism is not explicitly forbidden. Line 24 is the only of these commands directed at women, so that is a notable omission. 

“Do not defile yourselves by any of these things, for by all these the nations I am casting out before you defiled themselves; ²⁵ and the land became defiled, so that I punished its iniquity, and the land vomited out its inhabitants. ²⁶ But you shall keep my statutes and my ordinances and do none of these abominations, either the native or the stranger who sojourns among you ²⁷ (for all of these abominations the men of the land did, who were before you, so that the land became defiled); ²⁸ lest the land vomit you out, when you defile it, as it vomited out the nation that was before you. ²⁹ 

 Again, clearly, the real point of all this is to justify the Israelite's expropriation of Canaan. It is very unlikely that the Canaanites did not have similar proscriptions.

For whoever shall do any of these abominations, the persons that do them shall be cut off from among their people. ³⁰ So keep my charge never to practice any of these abominable customs which were practiced before you, and never to defile yourselves by them: I am the Lord your God.”

Footnotes:

1. Leviticus 18:17 Gk: Heb lacks your