en_tn/gen/32/12.md

But you said, 'I will certainly make you prosper. I will make your descendants ... number.'

This is a quotation within a quotation. It can be stated an an indirect quotation. Alternate translation: "But you said that you would certainly prosper me, and that you would make my descendants ... number" (See: rc://en/ta/man/translate/figs-quotesinquotes and rc://en/ta/man/translate/figs-quotations)

make you prosper

"do good to you" or "treat you well"

I will make your descendants like the sand of the sea

This speaks about the very large number of Jacob's descendants as if their number will be like the grains of sand on the seashore. (See: rc://en/ta/man/translate/figs-simile)

which cannot be numbered for their number

This can be stated in active form. Alternate translation: "which no one can count because of their number" (See: rc://en/ta/man/translate/figs-activepassive)