What does 'fully persuaded' mean in Romans 4:21?

Being fully persuaded means Abraham had no doubt that God would still do what He promised. He staggered not at the promise through unbelief but was strong in faith, convinced God was able to perform it, and his believing was imputed to him as righteousness.

Les explains that in Romans 4:21, being fully persuaded meant there was not an ounce of doubt in Abraham's mind that God was still going to do what He said He was going to do. Abraham was fully persuaded of what God had promised, and God was able also to perform it. His believing plus nothing was imputed—a bookkeeping term in the Greek—placed to his account on the ledgers of heaven, so he is now a righteous man.

Romans 4:21

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

What does it mean that Abraham was fully persuaded in Romans 4:21?

Being fully persuaded means Abraham had not an ounce of doubt that God would still do what He promised. He was strong in faith, giving glory to God, and trusted that God was able to perform what He had promised. His believing, plus nothing, was imputed to him as righteousness.