Why is Christ the response to Adam as the federal head of the human race?
Adam stands as the federal head of the human race, and when he fell, restoration was required. Christ is the response to that fallen headship as the second Adam, the Lord from heaven. The natural came first, then the spiritual; the earthy Adam brought the need, and Christ is the one who restores.
Les explains that every genealogy moves from the natural to the spiritual, and Paul makes this point by saying the spiritual was not first, but the natural, and afterward the spiritual. The first man, Adam, is of the earth and earthy, made from the dust. The second man is the Lord from heaven. As Adam is the federal head of the human race in Genesis, Christ is the response to that federal head because Adam fell. When Adam fell, there had to be some way of restoring it, and the second Adam, who is Christ, is the restorer. Les also offers a personal thought, not proved from Scripture, that before he sinned Adam may have had a body identical to Christ’s earthly appearance, since Adam was incorruptible and could have lived forever had he not fallen. Christ, however, did not fall.