That is not saying that when we sin, only our flesh is sinning.That what the gnostics claim.
They claim when they sin it was their body out doing sinful things but they themselves had nothing to do with it.
Nor that our soul was not involved with what the flesh initially desired to do.
A little knowledge can be used to try to impress others.
But it does just the opposite when that knowledge is misapplied and stumbled over.