25 But, say they, how is the flesh by a certain likeness compared unto the Church? What! Does the Church lust against Christ? Whereas the same Apostle said, “The Church is subject unto Christ.” Clearly the Church is subject unto Christ; because the spirit therefore lusts against the flesh, that on every side the Church may be made subject to Christ; but the flesh lusts against the spirit, because not as yet has the Church received that peace which was promised perfect.
And for this reason the Church is made subject unto Christ for the pledge of salvation, and the flesh lusts against the spirit from the weakness of sickness. For neither were those other than members of the Church, unto whom he thus spoke, “Walk in the spirit, and fulfill not the lusts of the flesh. For the flesh lusts against the spirit, and the spirit against the flesh; for these are opposed the one to the other; that you do not what we would.” These things were assuredly spoken unto the Church, which if it were not made subject unto Christ, the spirit would not in it lust against the flesh through continence.
By reason of which they were indeed able not to perfect the lusts of the flesh, but through the flesh lusting against the Spirit they were not able to do the things which they would, that is, not even to have the very lusts of the flesh. Lastly, why should we not confess that in spiritual men the Church is subject unto Christ, but in carnal men yet lusts against Christ? Did not they lust against Christ unto whom it was said, “Is Christ divided?” and, “I could not speak unto you as unto spiritual, but as unto carnal.
I have given unto you milk to drink as unto babes in Christ, not meat, for you were not as yet able; but not even now are you able: for you are still carnal. For whereas there is among you emulation, and strife, are you not carnal?” Against whom does emulation and strife lust, but against Christ? For these lusts of the flesh Christ heals in His own, but loves in none. Whence the holy Church, so long as it has such members, is not yet without spot or wrinkle. To these are added those other sins also, for which the daily cry of the whole Church is, “Forgive us our debts:” and, that we should not think spiritual persons exempt from these, not any one soever of carnal persons, nor any one soever of spiritual persons themselves, but he, who lay on the breast of the Lord, and whom He loved before others, says, “If we shall say that we have not sin, we deceive ourselves, and the truth is not in us.” But in every sin, more in what is greater, less in what is less, there is an act of lust against righteousness.
And of Christ it is written: “Who was made unto us by God, Wisdom, and Righteousness, and Sanctification, and Redemption.” In every sin therefore without doubt there is an act of lust against Christ. But when He, Who “heals all our sicknesses,” shall have led His Church unto the promised healing of sickness, then in none of its members shall there be any, even the very least spot or wrinkle. Then in no way shall the flesh lust against the spirit, and therefore there shall be no cause why the spirit also lust against the flesh.
Then all this conflict shall come to an end, then there shall be the highest concord of both substances; then to such a degree shall no one there be carnal, that even the flesh itself shall be spiritual. What therefore each one living after Christ does with his flesh, whereas he both lusts against its evil lust, which he restrains, hereafter to be healed, which he holds, not yet healed; and yet nourishes and cherishes its good nature, since “no one ever hated his own flesh,” this also Christ does with the Church, so far as it is lawful to compare lesser with greater matters.
For He both represses it with rebukes, that it burst not being puffed up with impunity; and raises it up with consolations, that it sink not being weighed down with infirmity. Hence is that of the Apostle, “For if we would judge ourselves, we should not be judged; but when we are judged, we are rebuked of the Lord, that we be not condemned with this world.” And that in the Psalm, “After the multitude of my griefs in my heart, Your consolations have gladdened my soul.” We are therefore then to hope for perfect soundness of our flesh without any opposition, when there shall be sure security of the Church of Christ without any fear.
Source: On Continence (New Advent)