3 For it is not one thing which dies and another which is quickened, as neither is it one thing which is lost and another which is found, but the Lord came seeking for that same sheep which had been lost. What was it, then, which was dead? Undoubtedly it was the substance of the flesh; the same, too, which had lost the breath of life, and had become breathless and dead. This same, therefore, was what the Lord came to quicken, that as in Adam we do all die, as being of an animal nature, in Christ we may all live, as being spiritual, not laying aside God's handiwork, but the lusts of the flesh, and receiving the Holy Spirit; as the apostle says in the Epistle to the Colossians: “Mortify, therefore, your members which are upon the earth.”
And what these are he himself explains: “Fornication, uncleanness, inordinate affection, evil concupiscence; and covetousness, which is idolatry.” The laying aside of these is what the apostle preaches; and he declares that those who do such things, as being merely flesh and blood, cannot inherit the kingdom of heaven. For their soul, tending towards what is worse, and descending to earthly lusts, has become a partaker in the same designation which belongs to these [lusts, viz., “earthly”], which, when the apostle commands us to lay aside, he says in the same Epistle, “Cast off the old man with his deeds.” But when he said this, he does not remove away the ancient formation [of man]; for in that case it would be incumbent on us to rid ourselves of its company by committing suicide.
Source: Adversus haereses (New Advent)