V. The Shorter Catechism-How Man Sinned: Q & A 13-15.
Q. 13 Did our first parents continue in the estate wherein they were created?
A. 13 Our first parents,-being left to the freedom of their own will,-fell from the estate wherein they were created,-by sinning against God.
Q. 14 What is sin?
A. 14 Sin is any wont of conformity unto,-or transgression of,-the law of God.
Q. 15 What was the sin whereby our first parents fell from the estate wherein they were created?
A. 15 The sin whereby our first parents fell from the estate wherein they were created, was their eating the forbidden fruit.
In Q & A 13 the catechism highlights three key points. One, our first parents had the freedom of will to choose life or death with the probation test in the garden. Adam and Eve were created in an estate of innocence, knowing no shame (Gen. 2:25). Two, death was the promised penalty for choosing to disobey God, and the tree of life could have equally been chosen (Gen. 3:6 Cf. Gen. 2:9; Eccl. 7:29). Part of this fallen condition is that humanity was no longer in a position to freely choose life (Gen. 3:22-23). Third, the cause of this fall is due completely to the will of humanity to choose death over life, to disobey the clear command of God (Gen. 2:17). Adam and Eve were given a law of prohibition, the penalty for disobeying which was death (Gen. 2:17).
John gave a perfect commentary on what took place by our first parents in the garden. “Sin is lawlessness” (I Jn. 3:4). This is what sin is. It is not simply the transgression of a law, as though somehow it is a failure just to live by one’s own code of conduct. It is the transgression of God the Creator’s law. Furthermore, it is not just the transgression of a law of His, but the failure also to conform to it in its entirety. “For whoever shall keep the whole law, and yet stumble in one point, he is guilty of all” (Js. 2:10 Cf. Rom. 7:7-12). Ignorance is also no excuse, because law by its very nature is a revelation from God, so that even those who do not have the law of Moses are nevertheless “a law to themselves” (Rom. 2:14). It is also not simply what one does, but also what one fails to do, as the law requires.