22 For the Lord chose Judas also among the apostles, and yet afterwards Judas betrayed the Lord. Yet not on that account did the faith and firmness of the apostles fail, because the traitor Judas failed from their fellowship: so also in the case in question the holiness and dignity of confessors is not immediately diminished, because the faith of some of them is broken. The blessed Apostle Paul in his epistle speaks in this manner: “For what if some of them fall away from the faith, shall their unbelief make the faith of God without effect?
God forbid: for God is true, though every man be a liar.” The greater and better part of the confessors stand firm in the strength of their faith, and in the truth of the law and discipline of the Lord; neither do they depart from the peace of the Church, who remember that they have obtained grace in the Church by the condescension of God; and by this very thing they obtain a higher praise of their faith, that they have separated from the faithlessness of those who have been associated with them in the fellowship of confession, and withdrawn from the contagion of crime. Illuminated by the true light of the Gospel, shone upon with the Lord's pure and white brightness, they are as praiseworthy in maintaining the peace of Christ, as they have been victorious in their combat with the devil.
Source: The Treatises of Cyprian (New Advent)