Sforno on Genesis 18:19/ספורנו על בראשית י״ח:י״ט

1כי ידעתיו, as a symbol of righteousness.

2למען אשר יצוה את בניו, G’d did all of the foregoing in order that Avraham would instruct his sons to emulate the ways of G’d having personal experience of G’d’s great love for mankind, seeing how His love extended even to the wicked.

3ושמרו...לעשות צדקה ומשפט למען הביא ה' על אברהם את אשר דבר אליו. The ultimate purpose of G’d in revealing to Avraham His manner of meting out justice was to ensure that He would have an opportunity to fulfill all the promises He had made to Avraham. [promises which were largely conditional on Avraham’s offspring being true to his teachings. Ed.] (compare 17,7)