Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned— 13for sin indeed was in the world before the law was given, but sin is not counted where there is no law. 14Yet death reigned from Adam to Moses, even over those whose sinning was not like the transgression of Adam, who was a type of the one who was to come.

15But the free gift is not like the trespass. For if many died through one man’s trespass, much more have the grace of God and the free gift by the grace of that one man Jesus Christ abounded for many. 16And the free gift is not like the result of that one man’s sin. For the judgment following one trespass brought condemnation, but the free gift following many trespasses brought justification. 17If, because of one man’s trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ.

18Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. 19For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous. 20Now the law came in to increase the trespass, but where sin increased, grace abounded all the more, 21so that, as sin reigned in death, grace also might reign through righteousness leading to eternal life through Jesus Christ our Lord.

In the last half of Romans 5, the comparison is made between what was lost in Adam and what is gained back in Christ (cf. Romans 5:12 and 5:18).  The point is that as one trespass led to condemnation, one act of righteousness led to justification and life (Romans 5:18).

1. In Romans 5:12, one finds that sin came into the world through one man, i.e. Adam.  The consequence for this sin was death – physical death (see Genesis 2:16-17 and 3:17-19, 22-24).  The consequence of Adam’s sin reached out to everyone – “to all men.”  This happened at a given point in the past as is indicated by the use of aorist tense verbs (dihlqen “spread” or “passed” and hmarton “sinned”) in the original Greek language.  That is, at the point in time that Adam sinned, humanity became universally doomed to physical death, even though all of humanity was not actually there when it happen.  This occurred in much the same way as when Levi, who was not yet born, “paid tithes to Melchizedek” (Hebrews 7:9-10).  In this scripture, Levi paid tithes to Melchizedek in a representative way through Abraham, even though Levi had not yet been born.  All of humanity sinned in a representative way through Adam even though almost all of it had not yet been born.  One should keep in mind that the consequence for this sin was physical death; spiritual death, due to sin, is a result of ones’ own actions (see Ezekiel 18:20; II Kings 14:6 and Romans 6:23).  The proof is in the fact that death reigned even before the law existed (Romans 5:13-14).  Just as Moses’ lifting up the serpent was a type of Christ being lifted up on a cross (see John 3:14-15; Numbers 21:9; John 8:28 and John 12:32) so was Adam a type of Christ (Romans 5:14).  Adam is the head of the physical race called humanity, just as Christ is the head of the spiritual race called disciples.
2. While there was loss (physical death) in Adam’s sin and gain in Christ’s death, it was not an equal trade.  There was “much more” (Romans 5:15 and 5:17) gained by Christ!  Because of Christ’s death, the physical death that was assigned to humanity at the time of Adam’s sin was erased as is evidenced by Christ’s resurrection (see I Corinthians 15:12-26 and 42-48).  This would be equal gain compared to the loss.  However, there will be those who receive an abundance of grace and the free gift of righteousness (Romans 5:17).  These are ones who will reign in eternal life through Jesus Christ (I Corinthians 15:53-56).
3. As sin reigned in death, grace also reigns through righteousness leading to eternal life through Jesus Christ our Lord (Romans 5:21