12 And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called. 13 And also of the son of the bondwoman will I make a nation, because he is thy seed.
Abraham was at an impasse, but in the midst of his conundrum God assured him it was alright to let Ishmael go. God assured Abraham that Ishmael would be under His protection and that He would raise the lad into a mighty nation of his own.
And this is a rehearsal for Abraham’s future sacrifice of Isaac. Here, with Ishmael, God is asking Abraham to turn his son over to God’s care, to surrender him with the trust that God will provide. Later Abraham will take that level of trust and surrender to a whole other level.