A.T. Robertson Commentary Romans 4:20

"yet, looking unto the promise of God, he wavered not through unbelief, but waxed strong through faith, giving glory to God," — Romans 4:20 (ASV)

He wavered not through unbelief (ου διεκριθη τη απιστια). First aorist passive indicative of old and common verb διακρινω, to separate, to distinguish between, to decide between, to desert, to dispute, to be divided in one's own mind. This last sense occurs here as in Mt 21:22; Mr 11:23; Romans 14:23; James 1:6. "He was not divided in his mind by unbelief" (instrumental case).

Waxed strong through faith (ενεδυναμωθη τη πιστε). First aorist passive again of ενδυναμοω, late word to empower, to put power in, in LXX and Paul and Ac 9:22.