8 You have written also, that on my account the Church has now a portion of herself in a state of dispersion, although the whole people of the Church are collected, and united, and joined to itself in an undivided concord: they alone have remained without, who even, if they had been within, would have had to be cast out. Nor does the Lord, the protector of His people, and their guardian, suffer the wheat to be snatched from His floor; but the chaff alone can be separated from the Church, since also the apostle says, “For what if some of them have departed from the faith?
Shall their unbelief make the faith of God of none effect? God forbid; for God is true, but every man a liar.” And the Lord also in the Gospel, when disciples forsook Him as He spoke, turning to the twelve, said, “Will you also go away?”then Peter answered Him, “Lord, to whom shall we go? You have the word of eternal life; and we believe, and are sure, that You are the Son of the living God.” Peter speaks there, on whom the Church was to be built, teaching and showing in the name of the Church, that although a rebellious and arrogant multitude of those who will not hear and obey may depart, yet the Church does not depart from Christ; and they are the Church who are a people united to the priest, and the flock which adheres to its pastor. Whence you ought to know that the bishop is in the Church, and the Church in the bishop; and if any one be not with the bishop, that he is not in the Church, and that those flatter themselves in vain who creep in, not having peace with God's priests, and think that they communicate secretly with some; while the Church, which is Catholic and one, is not cut nor divided, but is indeed connected and bound together by the cement of priests who cohere with one another.
Source: The Epistles of Cyprian (New Advent)