Through one that sinned (δι' ενος αμαρτησαντος). "Through one having sinned." That is Adam. Another contrast, difference in source (εκ).

Of one (εξ ενος). Supply παραπτωματος, Adam's one transgression.

Of many trespasses (εκ πολλων παραπτωματων). The gift by Christ grew out of manifold sins by Adam's progeny.

Justification (δικαιωμα). Act of righteousness, result, ordinance (Romans 1:32; Romans 2:26; Romans 8:4), righteous deed (Romans 5:18), verdict as here (acquittal).