We can see the difference between sin as a single act and the principle of sin very clearly in Adam's case. Let us note most carefully the penalty which God attached to Adam's transgression. Not a word is said of a change in his nature. All the penalty imposed was a twofold experience of death. This interpretation is fully confirmed, not only by the experience of Adam, but by that of all his posterity.
Humanity is now a dying race.
Their lives not only culminate in death, but they are vitiated by the gradual operation of death from birth to dissolution. We find that Adam, instead of fleeing from further errors, made more mistakes continually. One sin does not, in itself, constitute a sinner, but the one sin of Adam evidently led to his becoming such. Death entered through the one sin, and death it was that made him a confirmed sinner. He no longer needed a temptation from without.