How did Adam's action bring condemnation upon the entire human race?
Adam, as the federal head of the human race, acted on behalf of all humanity; his one offense plunged everyone into a place of condemnation. Through that one man’s offense, death began to reign over the race. Condemnation therefore came by representation, not by each person’s separate act.
Les explains that Adam was the federal head of the human race, so his offense was not merely personal. By that one man’s offense, death reigned, and Adam plunged everyone into a place of condemnation. The second man, the second Adam, has accomplished everything necessary to bring fallen man back to Himself. The only difference now is that there has to be an exercise of will.