21. Distrusting God—not eating the fruit—was Eve's sin.

When the woman saw that the fruit of the tree was good for food and pleasing to the eye, and also desirable for gaining wisdom, she took some and ate it. {Genesis 3:6a}

By the time Eve ate the fruit, she had become convinced that everything Satan had said was true — that God was a liar, that He was holding them back, that they could also be gods, equals, rivals. If she hadn’t bought into any of that, she would never have eaten the fruit, because on the other hand, God had told them that eating the fruit would lead to their death. So deciding which way to go was a life or death decision.

Eve chose to trust Satan instead of God. She chose to trust that what Satan claimed was true instead of trusting that what God said was true. If she had believed what God said, that eating the fruit would cause her to die, she wouldn’t have taken it and eaten it. But that’s not what she decided. She decided that (1) the fruit was good and (2) it would make her wise. This was in direct contradiction to what God had said, so in eating it, Eve was manifesting the choice she had made in her mind to believe that God was a liar and that He couldn’t be trusted. This was Eve’s sin. And that’s why she ate the fruit. Eating the fruit wasn’t the sin Eve committed. Eve ate the fruit because she had already sinned.

If you want to dig deeper—
Genesis 3
Romans 14:23