Charles Ellicott Commentary Genesis 17:18

"And Abraham said unto God, Oh that Ishmael might live before thee!" — Genesis 17:18 (ASV)

O that Ishmael ... — For thirteen years Ishmael had been the “son of the house” (Genesis 15:3) and was probably regarded as the true heir. Then, mingled with Abraham’s joy, there was also the pain, natural to a father, of knowing that this transfer of the promise to Sarah’s child meant the deposition and disappointment of one who for so long had held the post of honor.

Stoicism would have repressed this upright and natural feeling, but God hears and accepts the father’s prayers; and while the birthright and religious pre-eminence are justly given to the son of the freewoman, there is a large earthly blessing for the handmaid’s son.