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/jit/figs-quotesinquotes]] and [[rc://en/ta/man/jit/figs-quotations]])
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/jit/figs-simile]])
This can be stated in active form. Alternate translation: "which no one can count because of their number" (See: [[rc://en/ta/man/jit/figs-activepassive]])