Verse Comparison: Romans 4:21
American Standard Version
and being fully assured that what he had promised, he was able also to perform.
Amplified® Bible
Fully satisfied {and} assured that God was able {and} mighty to keep His word {and} to do what He had promised.
Darby English Version
and being fully persuaded that what he has promised he is able also to do;
International Standard Version
being absolutely convinced that God would do what he had promised.
King James Version
And being fully persuaded that, what he had promised, he was able also to perform.
Young's Literal Translation
and having been fully persuaded that what He hath promised He is able also to do: