The following was written in partial fulfillment of the requirements of Dr. Steve McKinion's Christian Theology II class at Southeastern Baptist Theological Seminary.
Topic: Why was it a sin to eat of the fruit of the tree of the knowledge of good and evil?
As Christians, we all recognize that Adam and Eve’s first sin in the garden of Eden prompted the catastropic Fall of all humanity, and that their eating of the fruit of the tree of the knowledge of good and evil was the act of sin that produced such horrific results in human history. What is perhaps less clear is why that particular act was sinful. Was it disobedience? gaining knowledge? pride? idolatry? The most straightforward reading of Genesis 3 makes it clear that the act was sinful at the most basic level because it was disobedience, a direct rejection of the stated will of God. God tells Adam that the consequences he receives are because he ate of the tree from which he was commanded not to eat (3:17).
Perhaps the more interesting question, then, is why disobedience to God is a sin. As Christians, we acknowledge that the Bible teaches us this truth. Digging deeper is helpful in understanding many things about God and the nature of both humanity and the shape of the world we inhabit. To describe why disobedience is sinful, though, requires that we first define what sin is. Sin is, at the most basic level, failure—missing the mark, as the Greek word would have it. The next question, then, is: Failure at what?
Sin is failure to be what humans were (and still are) meant to be—a mystery of ages, to which we have the answer. Genesis tells us exactly who we humans are. We are made in the image of God. We are to be small icons of divine glory. The divinity we are meant to recapitulate in miniature exists in perfect harmony, is completely wise and wholly good, and exercises utter sovereignty. Women and men are meant likewise to exist in true harmony, to be wise in right measure and truly good, and to exercise sovereignty in our appointed spheres. This is what it is to be human: to do as God does in the ways he appoints in the world he made.
Thus, to fail at that task is no small thing. It is to fail in the most significant way possible. Worse still, to fail as Adam and Eve did (and as we all have ever since) can only happen in a conscious act. Yes, our natures are now so corrupted that we all sin incidentally, too. But we all of us sin on purpose. Our first father and mother did not fail accidentally. They willfully rejected the very reason for their existence and spat in the face of the author of that existence. (Here is the source of the human struggle for existential meaning and the dread of meaningless that plagues us.) They rejected both the shape of reality and the one who made reality. They rebelled. They became traitors against the universe’s God.
Their sin, then, was not only disobedience. There are times when disobedience might be right: one should reject unjust commands. This, however, was not such a command. Their act of disobedience included both mistrust of most trustworthy God and self-exaltation over and against the only exalted God. God does not only demand our allegiance, he deserves it. He requires our worship not because he is vain, but because to worship anything else, however lovely, is to do injury to the object of that worship, to ourselves, and to the Triune Godhead. Adam and Eve’s eating of the fruit of the tree of the knowledge of good represented precisely that offense. They rejected God’s sovereignty, his wisdom and goodness, and even fellowship with him. They rejected their own sphere of sovereignty, chose quick knowledge over wisdom, deceit over goodness, and treachery over communion.