Why did God contradict himself?

Even God makes mistakes every now and then, it ain't like he's God. Oh wait nvrmind...

Deuteronomy was recording the rules of the Mosaic covenant. Before that people were coming to God merely through the promises given to Abraham and his offspring. There was a lot more grace in the original provision to Abraham, indeed some of his descendants behaved very badly and definitely needed grace. I agree with the view of St Paul in Galatians that the Mosaic Law was put in place to be like a schoolmaster, to keep people disciplined and in order, until the Messiah came, which was like coming into adulthood and one's inheritance. (Schoolmasters in those times were very tough.) If they didn't have some rules and rituals, tied in with blessings if they obeyed, they would maybe have soon forgotten about God and just worshipped the local baals and other gods. In which case God's attempt to get in relationship with mankind would have ended before the Messiah came.

There is no contradiction anywhere in scripture. What you have pointed out was done by Abraham, long before the Torah was officially given out at Mt. Sinai in Exod. 20. Nice try.

It's not a contradiction however he is now restricting the practice. In order to produce life, it had to happen for some time. Eventually it was not necessary.

They married before Abram's calling and Issac came on the scene much later.

Abraham was many, many years before the law of Moses and the incest law.

according to my source below sarai was really abraham's niece. Kind of complicated.

The different people who made up the Bible didn't always collaborate.

You're overlooking the fact that God doesn't actually exist.

He did not . At that time there was not any restrictions.