What is the whole plan of salvation?
God's plan of salvation rests on the law that the soul that sins must die, and all have sinned. Yet God provided a loophole: sinners need not die in themselves. By believing the gospel, Christ's substitutionary death takes their place, and the old Adam is crucified.
Les explains that this is the first fundamental law in Scripture: God told Adam not to eat of that one tree, and the day he ate he would surely die. That law is repeated—the soul that sinneth shall surely die—and Paul writes in Romans that all have sinned and come short of the glory of God. Since Adam sinned and every son of Adam sins, death must result; there is no getting around it. But God gave mankind a loophole: we have to die, yet we do not have to die in ourselves. We can take Christ's death as our substitution. So the plan of salvation is that although we must die because we are sinners, if we simply believe the gospel, Christ's death takes our place—the substitutionary death of Christ. He took my place and yours. That is why Paul teaches the old Adam has to be crucified and put to death, because he is a sinner; he that is dead is freed from old Adam.