Therefore, we know, which means, in truth, we have to admit and concede, that the Mosaic law does not cause sin, is not the invention of man, is not corrupt or carnal in any way, but is a part of the body of truth, which is of God, and therefore exists within the spiritual realm.
But we, as human beings, are of the carnal realm, or of the flesh realm.
That is the realm that is not spiritual, but is opposed to the spiritual realm.
Flesh is typically described as that of the sensual passions and propensities, and therefore is subject to corruption and decay. And as such, in the state of physical weakness, has a strong influence over the mind.
Without truth the mind of man has no defense against this overwhelming carnal state.
With truth, assuming that man learns truth, then there is a transformation of the mind, which, among other things, constructs an overwhelming defense against the carnal state.
And while man is in a state of carnality, and having committed sins, with no defense against sin, he is in a state of slavery, in subjection to a realm from which he cannot escape on his own.
The term sold, is an action that is caused by someone else.
So, when man is sold, man has no say over that sale, and therefore has to go to the buyer.
A slave has no say in his life or his destiny, but is in complete subjection to his owner.
Sin being the supreme owner of flesh, as it were, has complete control and authority.
Therefore, in order to escape sin, one cannot simply run away, but must be purchased out of sin by someone else.
And of course that someone else is Jesus Christ.