Genesis 20:13
And it came to pass, when God caused me to wander from my father’s house, that I said unto her, This is thy kindness which thou shalt shew unto me; at every place whither we shall come, say of me, He is my brother. And it came to pass, when God caused me to wander from my father’s house, that I said unto her, This is thy kindness which thou shalt shew unto me; at every place whither we shall come, say of me, He is my brother.
Abraham was explaining that when God caused him to wander from his father's house, he had made a standing arrangement with Sarah that at every place to which they came she should say of him that he was her brother, and this occurred during his sojourn among the Philistines. This was one of two occasions on which he passed Sarah off as his sister. The request grew out of fearfulness and unbelief, a failure to trust God's protecting care, though his faith was real and only not yet perfect.
The arrangement was an instance of lying and lack of truthfulness that stands condemned by God. It belongs to the account of Abraham's human attempts to manage God's promise by scheming that brought trouble rather than following God's plan, like his effort to bring about the promise through Hagar. At the same time it shows God's providential dealing with the family of Abraham as the chosen progenitor of the promised Seed, belonging to the history of beginnings and to the story of God's dealing with the Seed and the enemy's attempts to thwart His plan, in a book where God's law was in force and gospel promises and prophecies to His chosen shine, carrying forward the great facts of Creation, the Fall, the Seed, and the Deluge that run through the Bible.
The chapter is cited among examples showing that moral principles and knowledge of right and wrong existed before the law was given through Moses, including the prohibition of adultery which Abimelech understood through God's direct and clear instruction to him. The account presents Abimelech as knowing the true God and the Philistine nation as having a high regard for morality. In this chapter God used Abimelech to give Abraham a stern rebuke.