What does Genesis 20:10 mean?

Now therefore, restore the man’s wife. For he is a prophet, and he will pray for you, and you will live. If you don’t restore her, know for sure that you will die, you, and all who are yours.”

Abimelech rose early in the morning, and called all his servants, and told all these things in their ear. The men were very scared.

Then Abimelech called Abraham, and said to him, “What have you done to us? How have I sinned against you, that you have brought on me and on my kingdom a great sin? You have done deeds to me that ought not to be done!”

Abraham said, “Because I thought, ‘Surely the fear of God is not in this place. They will kill me for my wife’s sake.’

Besides, she is indeed my sister, the daughter of my father, but not the daughter of my mother; and she became my wife.

When God caused me to wander from my father’s house, I said to her, ‘This is your kindness which you shall show to me. Everywhere that we go, say of me, “He is my brother.”’”