40 Accordingly, He so now cleanses His Church by the washing of water in the word, that He may hereafter show it to Himself as not having spot, or wrinkle, or any such thing—altogether beautiful, that is to say, and in absolute perfection, when death shall be "swallowed up in victory." Now, therefore, in so far as the life is flourishing within us that proceeds from our being born of God, living by faith, so far we are righteous; but in so far as we drag along with us the traces of our mortal nature as derived from Adam, so far we cannot be free from sin. For there is truth both in the statement that "whosoever is born of God does not commit sin," and also in the former statement, that "if we say that we have no sin, we deceive ourselves, and the truth is not in us." The Lord Jesus, therefore, is both righteous and able to justify; but we are justified freely by no other grace than His. For there is nothing that justifies save His body, which is the Church; and therefore, if the body of Christ bears off the spoils of the unrighteous, and the riches of the unrighteous are laid up in store as treasures for the body of Christ, the unrighteous ought not therefore to remain outside, but rather to enter within, that so they may be justified.
41. Whence also we may be sure that what is written concerning the day of judgment, "Then shall the righteous man stand in great boldness before the face of such as have afflicted him, and made no account of his labors," is not to be taken in such a sense as that the Canaanite shall stand before the face of Israel, though Israel made no account of the labors of the Canaanite; but only as that Naboth shall stand before the face of Ahab, since Ahab made no account of the labors of Naboth, since the Canaanite was unrighteous, while Naboth was a righteous man. In the same way the heathen shall not stand before the face of the Christian, who made no account of his labors, when the temples of the idols were plundered and destroyed; but the Christian shall stand before the face of the heathen, who made no account of his labors, when the bodies of the martyrs were laid low in death. In the same way, therefore, the heretic shall not stand in the face of the Catholic, who made no account of his labors, when the laws of the Catholic emperors were put in force; but the Catholic shall stand in the face of the heretic, who made no account of his labors when the madness of the ungodly Circumcelliones was allowed to have its way. For the passage of Scripture decides the question in itself, seeing that it does not say, Then shall men stand, but "Then shall the righteous stand;" and they shall stand "in great boldness" because they stand in the power of a good conscience.
42. But in this world no one is righteous by his own righteousness—that is, as though it were wrought by himself and for himself; but as the apostle says, "According as God has dealt to every man the measure of faith." But then he goes on to add the following: "For as we have many members in one body, and all members have not the same office; so we, being many, are one body in Christ." And according to this doctrine, no one can be righteous so long as he is separated from the unity of this body. For in the same manner as if a limb be cut off from the body of a living man, it cannot any longer retain the spirit of life; so the man who is cut off from the body of Christ, who is righteous, can in no wise retain the spirit of righteousness, even if he retain the form of membership which he received when in the body. Let them therefore come into the framework of this body, and so possess their own labors, not through the lust of lordship, but through the godliness of using them aright. But we, as has been said before, cleanse our wills from the pollution of this concupiscence, even in the judgment of any enemy you please to name as judge, seeing that we use our utmost efforts in entreating the very men of whose labors we avail ourselves to enjoy with us, within the society of the Catholic Church, the fruits both of their labors and of our own.
Source: Letters (New Advent)