"It Behooved Us to Withdraw"
Now they treat us as persons guilty of schism and heresy because we preach a doctrine unlike theirs, do not obey their laws, and hold our separate assemblies for prayers, baptism and the celebration of the Supper, and other holy activities.
This is indeed a very grave accusation but one that needs no long and labored defense. Those who, by making dissension, break the communion of the church are called heretics and schismatics. Now this communion is held together by two bonds, agreement in sound doctrine and brotherly love. Hence, between heretics and schismatics Augustine makes this sort of distinction: heretics corrupt the sincerity of the faith with false dogmas; but schismatics, while sometimes even of the same faith, break the bond of fellowship.
But it must also be noted that this conjunction of love so depends upon unity of faith that it ought to be its beginning, end, and, in fine, its sole rule. . . . Apart from the Lord's Word there is not an agreement of believers but a faction of wicked men. (IV.2.5)
Now let them go and shout that we who have withdrawn from their church are heretics, since the sole cause of our separation is that they could in no way bear the pure profession of truth. . . . It is enough for me that it behooved us to withdraw from them that we might come to Christ.
John Calvin, Institutes of the Christian Religion, Book IV, Chapter 2, paragraphs 5 and 6.