Romanos 4

Pienissimamente persuaso, che, qualunque cosa abbia promesso, egli è potente ancora per farla.

Plenamente convencido de que todo lo que había prometido, era también poderoso para hacerlo.

And being fully persuaded that, what he had promised, he was able also to perform.

and being fully assured that what he had promised, he was also able to perform.