John Calvin Commentary Genesis 17:20

"And as for Ishmael, I have heard thee: behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation." — Genesis 17:20 (ASV)

And as for Ishmael. He here more clearly distinguishes between the two sons of Abraham. For in promising to the one wealth, dignity, and other things pertaining to the present life, He shows him to be a son according to the flesh. But He makes a special covenant with Isaac, which rises above the world and this frail life: not to cut Ishmael off from the hope of eternal life, but to teach him that salvation is to be sought from the descendants of Isaac, where it truly dwells.

We infer, however, from this passage that the holy fathers were by no means kept down to earth by the promises of God, but rather were borne upwards to heaven. For God liberally and profusely promises to Ishmael whatever is desirable with respect to this earthly life; and yet He accounts as nothing all the gifts He confers on him, in comparison with the covenant which was to be established in Isaac.

It therefore follows that neither wealth, nor power, nor any other temporal gift is promised to the sons of the Spirit, but an eternal blessing, which is possessed only by hope in this world. Therefore, however we may now abound in delights and in all good things, our happiness is still transient, unless by faith we penetrate into the celestial kingdom of God, where a greater and higher blessing is laid up for us.

It is, however, asked whether Abraham considered only this earthly life when he prayed for his son. For the Lord seems to intimate this when He declares that He had granted what Abraham asked, and yet only mentions the things we have recorded. But it was not God’s design to fulfill Abraham's entire wish on this point; He only makes it plain that He would show some regard for Ishmael, for whom Abraham had entreated, so as to show that the father's prayer had not been in vain. For He meant to testify that He embraced Abraham with such love that, for his sake, He showed regard for his whole lineage and dignified it with special benefits.