Jesus’ title “the Second Adam” is explained in two chapters: in Romans 5, and in 1 Corinthians 15.
Romans 5 teaches us that Adam was “a pattern of the one to come” (Romans 5:14). This means that Adam’s life set a pattern, and then, when Jesus came, Jesus followed that same pattern. However, whereas Adam disobeyed God and brought sin and death into the world, Jesus obeyed God so that the world could receive God’s free gift of righteousness and eternal life. The parallels between Jesus and Adam described in Romans chapter 5 are summarized in the diagram below.
1 Corinthians 15 focuses on the end of this diagram, and, in the light of Jesus’ resurrection, develops the contrasts between “death through Adam” and “life through Christ”, explaining that, “since death came through a man, the resurrection of the dead also comes through a man. For as in Adam all die, so in Christ all will be made alive” (1 Corinthians 15:21-22).
Then, to teach us about the Christian’s future resurrection body, 1 Corinthians 15:44-54 compares and contrasts Adam and Jesus once again. Adam came from “the dust of the earth”, but Jesus comes “from heaven”. Since we are descended from Adam, we currently live in the same kind of “natural” and “earthly” body that Adam had; but, when Jesus returns, we “will be changed”, as our current “perishable” and “mortal” bodies transform instantly into new “imperishable” and “immortal”, “spiritual” and “heavenly” bodies. For, “just as we have borne the likeness of the earthly man, so shall we bear the likeness of the man from heaven” (1 Corinthians 15:49).
All of these theological truths are summed up in Jesus’ title: “the Second Adam.”