Some wonderful words from Augustine on the justice of God's punishment of the first sin:
This punishment was neither excessive nor unjust. Anyone who thinks otherwise merely proves his inability to measure the magnitude of this sinfulness in a case where sin was so easy to avoid. For, just as the obedience of Abraham is rightly regarded as magnificent precisely because the killing of his son was a command so difficult to obey, so in Paradise the lack of obedience was so lamentable because the prohibition imposed was so easy to respect. And just as the obedience of the Second Man is so marvelous because He made Himself obedient unto death, so is the disobedience of the first man so malignant because he made himself disobedient unto death. It was the Creator Himself who commanded; the thing commanded was perfectly easy; the penalty attached was known to be great. Surely, then, the malice is incalculable when the creature defies, in a matter so simple and in the face of so fearful a penalty, the supreme authority of Omnipotence.We deserve exactly what we get, because our offense is so great. That we don't think it great is yet another sign of the depths of our disobedience. This just punishment is not something that comes to or from the body alone, but is something which is connected to the whole person, body and soul in harmony (if we can use the word "harmony" when talking about sin). We see this in many of the sins in which we regularly engaged, even the ones we think of as strictly bodily.
Lust is a great example of this, sometimes driving the soul and sometimes being driven by it, and sometimes refusing to obey all together.