I did not include this in my Incest in The Bible Study because while it's relevant I don't consider Incest the main concern here, but rather Rape.
It's important to remember the Chapter Titles you often see in modern Bibles are not part of the original inspired text. And I'm reminded of this every time I see a Bible name this part of II Samuel "Incest in David's House", when clearly it's Rape not Incest that is the greater focus of the story.
No, I'm not saying that because I have a modern bias of seeing Rape as the most unforgivable offense. I'm saying that because without the context of the rest of The Bible, we wouldn't even know from this narrative alone that Brother-Sister incest wasn't allowed in Ancient Israel.
Why do I say that? Verses 12-13 Tamar says "Nay, my brother, do not force me; for no such thing ought to be done in Israel:
do not thou this folly. And I, whither shall I cause my shame to go? and as for thee, thou shalt be as
one of the fools in Israel. Now therefore, I pray thee, speak unto the king; for
he will not withhold me from thee."
Pretty telling detail, it seems as if she expects David would have allowed such a marriage if Amnon had gone after it in a proper fashion.
How do we explain that line in the Context of what we know from Leviticus and Deuteronomy? Mostly I think she may just be saying whatever she can think of to get him to stop. But other theories could be provided.
I'm emphasizing this not to lessen how much of a Sin Brother-Sister Incest is. But because certain skeptics of The Bible have an obsession with making it seem like The Bible is okay with Rape.
Yes, the parts of Israel's Civil Law code dealing with the issue are not ideal to the modern World. No Ancient Culture's was. But first and foremost I can simply point to the Golden Rule. And then there is this incident, and Genesis 24, as well as Sodom and Gomorrah, which was about Gang Raping Immigrants, NOT Homosexuality. The Law of Moses was imperfect.