How did Adam's sin condemn the whole human race?
Adam's single act of disobedience—eating the forbidden fruit—plunged the entire human race into condemnation. As the federal head of humanity, his rebellion made every person, beginning with Cain, a fallen creature. Thus all are condemned by virtue of his act, not their own first sin.
Les teaches that Adam, as the first man, committed a simple act of disobedience by eating the forbidden fruit, and that act plunged the whole human race into condemnation. Every human being, beginning with Cain, has been a fallen creature by virtue of Adam's act of rebellion. Adam served as the federal head of the whole human race, so his disobedience brought everybody into that place of condemnation. But God did not leave it there. He brought the second man, Christ, making it possible for every degenerate son of Adam to become a regenerate son of God. Les connects this to 1 Corinthians 15:45, where the first Adam was made a living soul, and the last Adam, Jesus Christ, became a quickening spirit—meaning life-giving. He also references Ephesians 2:1, where those dead in trespasses and sins were quickened, made alive.