Adam and Eve fell into sin. The fall is really not what the word implies at all. It is not a downward plunge to some lower level in the great chain of being, some lower rung on the ladder of morality and freedom. Rather it is an upward rebellion, an invasion of the realm of things "above," the usurping of divine prerogative. To retain traditional language, one would have to resort to an oxymoron and speak of an "upward fall." This, after all, is precisely what the temptation by the serpent in the garden implies: "You will not die... you will be like God, knowing good and evil" (Genesis 3:4-5). A line had been drawn over which Adam and Eve were not to step. They were not to eat of the tree of knowledge of good and evil. There was a realm "above" which they were to leave to God; if they did not, their death would result. But the tempter insinuated, "Don't believe it for an instant! God is only jealous of the divine preserve! God knows that if you step over the line you will not die but become gods. You have something going for you! You have divine qualities, you have an immortal soul." So the step is taken. It is rebellion, an upward fall.
The first Adam ventured up into the "realm of things above" and brought death. The second Adam ventured down into the "realm of things below" and brought life.
The temptation for Christian's is to think that once God saves us we move beyond the First Adamic impulse to fall upward. The truth is, however, that even after God saves us we continue to fall upward--trying to claim for ourselves (in such subtle ways) the glory that belongs to God alone; trying to secure for ourselves the rescue that God alone can provide. "The essence of sin is man substituting himself for God, while the essence of salvation is God substituting himself for man. Man asserts himself against God and puts himself where only God deserves to be; God sacrifices himself for man and puts himself where only man deserves to be." (Stott)