en_tn/rom/04/18.md

In hope he believed against hope

This idiom means that Abraham hoped and believed even though what he hoped for seemed to be impossible. That is, Abraham trusted God to give him many descendants, even though it seemed to be impossible for him to have children. Alternate translation: "Even though it seemed that there was no reason to hope, Abraham hoped and believed" or "Even though it seemed to be impossible for him to have descendants, Abraham believed God and confidently expected" (See: rc://en/ta/man/jit/figs-idiom and rc://en/ta/man/jit/figs-explicit)

according to what he had been told

You can translate this in an active form. Alternate translation: "just as God said to Abraham" (See: rc://en/ta/man/jit/figs-activepassive)

So will your descendants be

The full promise God gave to Abraham can be made explicit. Alternate translation: "You will have more descendants than you can count" (See: rc://en/ta/man/jit/figs-explicit)