What does Romans 5:18 mean?

Paul summarizes the ideas he has been discussing since the beginning of this section in verse 12. One trespass, one sin, led to the condemnation of all men. This was Adam's sin in breaking God's command not to eat from one specific tree. In doing so, he introduced sin and death to the world, where they took root in every person to follow. Because all sinned, all faced God's judgment and the same fate: condemnation.

By contrast, though, one "act of righteousness" leads to the opportunity for justification for every person in the world. This act of righteousness was Jesus' death on the cross to pay for human sin. Those who, by faith, receive this free gift of God's grace are declared righteous by God. They are justified. This is the case Paul has been making throughout Romans.

Some read the words "for all men" here to mean that all people are justified by Christ's death on the cross no matter what. In other words, even faith in Christ is not required to be saved from God's wrath; all people will simply find themselves justified and saved, no matter what they do or believe. This is known as "universalism," but it cannot be reconciled with what Paul teaches throughout Romans and throughout the New Testament. Even in the previous verse, Paul insists that God's abundant grace is specifically for those who receive it, by faith.