The Westminster Shorter Catechism

Q15. What was the sin whereby our first parents fell from the estate
wherein they were created?

A. The sin whereby our first parents fell from the estate wherein they were created,
was their eating the forbidden fruit.[1]

Proofs

[1] Genesis 3:6, 12.

Comments

The question appears so straight forward that there hardly needs to be any comments: The sin by which our first parents fell, by which they also involved their entire posterity in sin, was their disobedience to God’s positive commandment to them not to eat of the Tree of the Knowledge of Good and Evil.

A few comments are helpful though. Firstly, it must be noted that the fruit itself is not intrinsically evil. Neither is there anything magical about it. It was probably just an ordinary fruit tree, and had God not issued a prohibition to Adam and Eve, eating of it would have been a matter of indifference. But since God issued the commandment to them to try their obedience, eating of the fruit became absolutely unlawful, so that when Adam and Eve ate of it, they were essentially rebelling against God. Secondly, if we think about it carefully, we will see that this sin involves much more than a simple breaking of a positive command. Thomas Vincent is especially helpful here in his enumeration of what sins were included with Adam and Eve’s disobedience. He writes:

The sins included in our first parents, eating the forbidden fruit were: (1) Rebellion against God their sovereign, who had expressly forbidden them to eat of this tree. (2) Treason, in conspiring with the devil, God’s enemy, against God. (3) Ambition, in aspiring to a higher state, namely, to be as God. (4) Luxury, in indulging so much to please the sense of taste, which did inordinately desire this fruit. (5) Ingratitude to God, who had given them leave to eat of any tree of the garden besides. (6) Unbelief, in not giving credit to the threatening of death, but believing the devil, who said they should not die, rather than God, who told them they should surely die, did they eat of this fruit. (7) Murder, in bringing death, by this sin, upon themselves, and all their posterity. These, and many other sins, were included in this sin of our first parents, eating of the forbidden fruit; which did render it exceeding heinous in the sight of God.