Genesis 18:19 - Ellicott's Commentary On The Whole Bible

For I know him, that he will. — This translation has most of the Versions in its favour, and means that Abraham’s good conduct earns for him the Divine condescension. But the Hebrew is, For I have known him in order that he may command his sons, &c. It gives God foreknowledge of the purpose for which He had called Abraham as the reason for thus revealing to him the method of the Divine justice. And this purpose was, that from Abraham should spring a nation whose institutions were to be fraught with Divine truth, whose prophets were to be the means of revealing God’s will to man, and of whom, as concerning the flesh, the Messiah should come. What more fitting than that one appointed to fill so noble a calling should also be raised to the rank of a prophet, and be permitted to share in the Divine counsels? This rendering closely agrees with what is said in Genesis 18:18 about Abraham growing into a mighty nation; and it was the unique and high purpose for which this nation was to be called into being which brought Abraham into so close a relation to Jehovah.