Reconciliation is the issue. Let us tear this apart. The chapter is talking about two people. It is talking about Adam and what he did, and how it affected mankind. The other one of course is Jesus Christ—what He did and how it affects mankind. It is not really a comparison, but a contrast that is going on here between the two of them.
Catholic doctrine of original sin says that we are all tainted by evil (by an evil nature), and death passes on to us because of Adam's sin. We have been affected by what Adam did, but not in the Catholic way.
What we are looking at here is a judgment by God. You will notice as we read that the word 'judgment' appeared at least three times. Verse 16: "For the judgment which came from one offense. . ." Who made that judgment? God made the judgment. We are looking at a judgment of God. Adam was the test case. He was the first man. He was the representative man, and what God judged was that as Adam went, so also would all of mankind. Mankind would just follow.
Now here comes one of the more difficult things. God judged things in this way: when Adam sinned, the entire race of mankind sinned in Adam. There is a practical explanation for this. Adam carried all of the genes and chromosomes, from which all of the rest of mankind would be created, in his body. So when Adam sinned, everybody sinned and God's judgment was that death therefore passed upon all men because Adam sinned.
Now back to Romans 5:15—actually we are just picking it up from there. God's solution to bridging the gap was as follows: just as mankind was cut off from God through one man, so would mankind be reconciled to God through one Man. But there are contrasts. Adam's sin and death ultimately affected man more or less automatically because it is the easy way to go—the broad way to go.
Christ, on the other hand, followed the straight and the narrow. He lived righteously and He died. His death is more than sufficient to cover all of the sins of all of mankind in order that reconciliation might be effected. But what He did does not pass upon mankind automatically, and there is the difference, because unless God reveals Himself and people believe and repent, reconciliation cannot occur.
