Genesis 20:10-11

Of course Sarah was probably a very beautiful woman, and Abimelech, as king in that area, would have liked to have had her as part of his harem, and Abraham told a half-truth. “She is my sister.” Actually, she was a half sister. They had the same father, but different mothers, and so he did not completely lie, but when he was nailed down by Abimelech—“Why did you say that?”—Abraham had to confess, well basically, “It was to save my own skin.”

The instruction for you and me is this. When Abraham was saying, “The fear of God is not in this place,” he connected the possibility that he would be murdered to the fact that he could detect that the fear of God was not in that place. In other words, where there is no fear of God, sin follows right on its heels. It is the fear of God, not just faith, that stops us from sin.

Genesis 20:1-13

Now here we get the whole story and the reason why Abraham wanted to call Sarah his sister. Of course she is beautiful, and he felt that the fear of God was not in the general area; that his life would be in danger, he could be killed. So he believed his life was in the balance because of his beautiful wife and because kind of, sort of, well, maybe, she was slightly his sister, she actually, really, kind of was, but regardless of these things, God was not happy. In God's infinite wisdom and kindness, He does intervene and saves Abimelech from sin. Here we see that Abraham offended both Pharaoh and Abimelech by intentionally putting them in a situation where sin could occur. He was thinking about himself and not others.