Charles Ellicott Commentary Romans 5:20

"And the law came in besides, that the trespass might abound; but where sin abounded, grace did abound more exceedingly:" — Romans 5:20 (ASV)

Entered.—A graphic metaphorical expression: “Came in to the side of” the sin already existing; “took its place,” as it were, “by the side of” sin, and joined forces with it, thus greatly adding to its extent and power.

Abound.—This word should be reserved for the last of the three places in this verse in which it appears in the Authorised version. The original in the other two places is different, and has the force of “Might be multiplied,” or “increased”—i.e., made more and made worse.

On verses 20, 21:

The Apostle had already (Romans 5:13–14) alluded to the intervention of the Law. Now he returns to the topic, and in order to complete his historical view of the origin of sin through Adam, and its atonement through Christ, he considers what was its effect upon the former, and how that effect was met and neutralised by the latter.

Mankind had already been led into sin by Adam. The Law came in to make matters still worse. It substituted conscious sin for unconscious, and so heightened its guilt. But all this is more than retrieved by grace.