en_tn/heb/11/11.md

It was by faith

The abstract noun "faith" can be expressed with the verb "believe." Possible meanings are 1) it was by Abraham's faith. AT: "It was because Abraham believed God" or 2) it was by Sarah's faith. AT: "It was because Sarah believed God" (See: rc://en/ta/man/translate/figs-abstractnouns)

received ability to father a child

"received ability to become a father" or "received ability to have a child"

since he considered as faithful the one who had given the promise

"because he believed God, who had give the promise, to be faithful"

almost dead

"too old to have children" or "very old"

descendants as many as the stars in the sky and as countless as sand by the seashore

This simile means Abraham had very many descendants. (See: rc://en/ta/man/translate/figs-simile)

as countless as sand by the seashore

This means that just as there are so many grains of sand on the seashore that no one can count them all, Abraham had so many descendants that no one can count them all.