From
newadvent.org/cathen/01129a.htm
More important is the theological doctrine formulated by St. Paul in Romans 5:12-21, and in 1 Corinthians 15:22-45. In the latter passage Jesus Christ is called by analogy and contrast the new or “last Adam.” This is understood in the sense that as the original Adam was the head of all mankind, the father of all according to the flesh, so also Jesus Christ was constituted chief and head of the spiritual family of the elect, and potentially of all mankind, since all are invited to partake of His salvation.** Thus the first Adam is a type of the second**, but while the former transmits to his progeny a legacy of death, the latter, on the contrary, becomes the vivifying principle of restored righteousness. Christ is the “last Adam” inasmuch as “there is no other name under heaven given to men, whereby we must be saved” (Acts 4:12); no other chief or father of the race is to be expected. Both the first and the second Adam occupy the position of head with regard to humanity, but whereas the first through his disobedience vitiated, as it were, in himself the stirps of the entire race, and left to his posterity an inheritance of death, sin, and misery, the other through his obedience merits for all those who become his members a new life of holiness and an everlasting reward.** It may be said that the contrast thus formulated expresses a fundamental tenet of the Christian religion and embodies in a nutshell the entire doctrine of the economy of salvation**