Римлянам 5:15

But--"Yet," "Howbeit." not as the offence--"trespass." so also is the free gift--or "the gracious gift," "the gift of grace." The two cases present points of contrast as well as resemblance. For if, &c.--rather, "For if through the offense of the one the many died (that is, in that one man's first sin), much more did the grace of God, and the free gift by grace, even that of the one man, Jesus Christ, abound unto the many." By "the many" is meant the mass of mankind represented respectively by Adam and Christ, as opposed, not to few, but to "the one" who represented them. By "the free gift" is meant (as in Rom 5:17) the glorious gift of justifying righteousness; this is expressly distinguished from "the grace of God," as the effect from the cause; and both are said to "abound" towards us in Christ--in what sense will appear in Rom 5:16-17. And the "much more," of the one case than the other, does not mean that we get much more of good by Christ than of evil by Adam (for it is not a case of quantity at all); but that we have much more reason to expect, or it is much more agreeable to our ideas of God, that the many should be benefited by the merit of one, than that they should suffer for the sin of one; and if the latter has happened, much more may we assure ourselves of the former [PHILIPPI, HODGE].

The apostle, having made good his point, and fully proved justification by faith, in this chapter proceeds in the explication, illustration, and application of that truth. I. He shows the fruits of justification (Rom 5:1-5). II. He shows the fountain and foundation of justification in the death of Jesus Christ, which he discourses of at large in the rest of the chapter.

5:15 Paul uses the word many in contrast with one. Many does not always mean all, but it can include all people if the context suggests it. Clearly, the many who suffer death because of Adam includes everyone (see 5:12), but Paul makes it clear elsewhere that the many who receive the gift of forgiveness through Jesus Christ, sadly, does not include everyone (see 11:1-5).