Incest in the Bible

"Cursed be he that lieth with his sister, the daughter of his father, or the daughter of this mother..."
Deuteronomy 27:22

"And if a man shall take his sister, his father's daughter, or his mother's daughter...it is a wicked thing...."
Leviticus 20:17

Yet Abraham marries his father's daughter and remains God's favorite:

"And Abraham said, Because I thought, Surely the fear of God is not in this place; and they will slay me for my wife's sake. And yet indeed she is my sister; she is the daughter of my father, but not the daughter of my mother; and she became my wife."
Genesis 20:11-12