John Gill Commentary Genesis 32:12

"And thou saidst, I will surely do thee good, and make thy seed as the sand of the sea, which cannot be numbered for multitude." — Genesis 32:12 (ASV)

And you said, I will surely do you good
All kind of good, most certainly and constantly; so Jacob rightly interpreted the promise, "I will be with thee", (Genesis 31:3) ; for the promise of God's presence includes and secures all needful good to his people; and from this general promise Jacob draws an argument for a special and particular good, the preservation of him and his family, he was now pleading for; and the rather he might hope to succeed, since the following promise was also made him: and make your seed as the sand of the sea, which cannot be numbered for
multitude ;
which could not be fulfilled, if he and his family were cut off at once, as he feared; but God is faithful who has promised.