How did Adam's role as head of the human race affect us?
Adam served as the head of the natural human race, and his role plunged us into sin. That sin precipitated death, so his headship brought sin and death to all his descendants. Scripture sets him as one federal head, contrasted with the last Adam, the life-giving spiritual head.
Les explains that Scripture presents two federal heads. Adam is the head of the natural progeny of the human race, and as that head he plunged us into sin; sin then precipitated death. So Adam's role affected humanity by bringing sin and the death that follows it. Les compares Scripture with Scripture and turns to I Corinthians 15:45-46, where the first man, Adam, was made a living soul, while the last Adam was made a quickening, or life-giving, spirit. The first is natural and earthy; afterward comes the spiritual, the second man, the last Adam, the Lord from heaven. Les also directs attention to Romans 5:12.
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned: