In this passage it shows that “The Law came in so that the transgression would increase; but where sin increased, grace abounded all the more,” Rom 5:20 (NASB) The general effect that the Law has on mankind is to reveal sin. Because of the fall, sin is the master or ruler …. it is said to reign in death.

However when, by God’s grace, people receive a righteousness (i.e. as if they had kept the Law perfectly) through faith in Christ, it sets them free forever from having sin as their master…. “so that, as sin reigned in death, even so grace would reign through righteousness to eternal life through Jesus Christ our Lord.” Rom 5:21 (NASB)