And Abimelech said unto Abraham,.... Continuing his discourse with him:

what sawest thou, that thou hast done this thing? he desires to know what he had observed, either in him or his people, that gave him any reason to conclude that they were a lustful people, and would stick at nothing to gratify their lusts, which put him upon taking such a method to secure his life, lest they should kill him for his wife's sake.

"What sawest thou," i.e., what hadst thou in thine eye, with thine act (thy false statement)? Abimelech did this publicly in the presence of his servants, partly for his own justification in the sight of his dependents, and partly to put Abraham to shame. The latter had but two weak excuses: (1) that he supposed there was no fear of God at all in the land, and trembled for his life because of his wife; and (2) that when he left his father's house, he had arranged with his wife that in every foreign place she was to call herself his sister, as she really was his half-sister. On the subject of his emigration, he expressed himself indefinitely and with reserve, accommodating himself to the polytheistic standpoint of the Philistine king: "when God (or the gods, Elohim) caused me to wander," i.e., led me to commence an unsettled life in a foreign land; and saying nothing about Jehovah, and the object of his wandering as revealed by Him.

And Abimelech said unto Abraham, What sawest thou, that thou hast done this thing?

20:10 What sawest thou that thou hast done this thing - What reason hadst thou to think, that if we had known her to be thy wife, thou wouldst have been exposed to any danger by it?

20:9-13 See here much to blame, even in the father of the faithful. Mark his distrust of God, his undue care about life, his intent to deceive. He also threw temptation in the way of others, caused affliction to them, exposed himself and Sarah to just rebukes, and yet attempted an excuse. These things are written for our warning, not for us to imitate. Even Abraham hath not whereof to glory. He cannot be justified by his works, but must be indebted for justification, to that righteousness which is upon all and unto all them that believe. We must not condemn all as hypocrites who fall into sin, if they do not continue in it. But let the unhumbled and impenitent take heed that they do not sin on, thinking that grace may abound. Abimelech, being warned of God, takes the warning; and being truly afraid of sin and its consequences, he rose early to pursue the directions given him.