Matthew Poole and continuators on Romans 5:21

21 That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord .

Before he ascribed Dominion and Raign to Death, now to Sinners; the reason is evident, because death indeed reigneth by sin. Before also he had made the comparison betwixt Adam and Christ, here 'tis betwixt sin and grace, the power of one and of the other. The summe is, that as Sin hath prevailed over all mankind to bring death upon man, not only a temporal but eternal death, so the grace of Christ prevails, and becomes effectual to confer upon us eternal Life.

i. e. Imputed or imparted.

See how sweetly the end answers the beginning of this Chapter, and how Jesus Christ is both the Author and Finisher of all.