John Calvin Reformed @genevareformer

3. And Abram fell on his face We know that this was the ancient rite of adoration. Moreover, Abram testifies, first, that he acknowledges God, in whose presence all flesh ought to keep silence, and to be humbled; and, secondly that he reverently receives and cordially embraces whatever God is about to speak.

Matthew Henry Presbyterian @wholebiblehenry

Here is, I. The time when God made Abram this gracious visit: When he was ninety-nine years old, full thirteen years after the birth of Ishmael. 1. So long, it should seem, God's extraordinary appearances to Abram were intermitted; and all the communion he had with God was only in the usual was of ordinances and providences.

Commenting on Genesis 17:1-3

John Gill Reformed Baptist @doctorgill

And Abram fell on his face,.... At the sight of so glorious a Person that appeared to him, and in reverence of his majesty, and as sensible of his unworthiness of such a visit, and of having such favours bestowed upon him; and not because he was not as yet circumcised, as the Targum of Jonathan expresses it; and so other Jewish (f) writers observe...