RobH_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. Alternate translation: "It was because Abraham believed God" or 2) it was by Sarah's faith. Alternate translation: "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"