And he said, &c.— One only speaks, the superior person, when the Divine promise is renewed: and the authoritative manner in which he speaks, confirms our opinion on Genesis 18:1 and ch. Genesis 16:7. I will certainly return to thee, according to the time of life, or at this time in the next year. Some of the ancient versions perfectly agree with this interpretation, which I believe to be the best: and Genesis 16:14 seems to explain it in some measure.
Related Commentaries of Genesis 18:10
Genesis 18:10
10 And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.