Why did God decide at the time of Moses that you couldn't get it on with your sister anymore?

A devilish question I admit!

I have had the same type of question lately. Why did God get so angry with Israelites for making idols and worshipping false gods, when Jacob had two wives who stole their fathers household gods and took them with them when Jacob left his father-in-law? There is nothing in Genesis indicating God being angry with his wives for taking these idols either...but low and behold, from Exodus onward, if you bowed down to any foreign god or idol or worshipped the Ashera Poles (yeah, a female fertility pole) or built an altar to a false god - woe be it unto you!

Apparently, the only answer I have in response to this, and your question is, that the Covenant established with Moses was a New Covenant (while the New Covenant INCLUDED the prior promises that God had made to Abraham and his line that his ancestors would inherit the Land of Milk and Honey and that his ancestors would be greater than all the stars in heaven and all the grains of sand in the world). Apparently, as long as Abraham did what was right under the limited conditions of the Limited Covenant at THAT time differs from the New Covenant given to Moses which included a lot more demands and requirements. Remember, God had not given Abraham the 10 Commandments either and so Abraham was not bound by them.

You can, you just can't marry them.

Every dad has a favourite. Abraham was that. After all, they call Yahweh "the God of Abraham." Wrapped around Abe's little finger he is.

It was of course to stop the re-emergence of the Neanderthal style rock apes that this sort of DNA corrupting behaviour ultimately creates, this theory is further vindicated by God's relatively relaxed indifference to isolated folks still doing their sisters up the poopsie

Here's my theory: God must've tried incest Himself and then realized how much better than non-incest it was. He probably thought to Himself, "Geez, this is way too much fun, I'd better ban it on Earth and only the Mormons who make it to Heaven will experience the delight of a siblings genitals"

one of the big three of the basketball Over Time, the other being Dennis Rodman and Scottie Pippen.

Generations of sin corrupted DNA.

Least that's what I've heard.

because he realized that the humans' genes were being messed up by all the inbreeding, and that humans would not evolve well if they were constantly inbreeding.

The Lard knows that the more inbred people are the more they will believe in him.

Too much hemophilia in the blood line hnnm......

Cuz the genes, they were gettin' tired out.