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.
Related Commentaries of Romans 5:20
Romans 5:20-21
20 Moreover the law entered, that the offence might abound. But where sin abounded, grace did much more abound:
21 That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord.