John Calvin explains why Christians must work for unity within the church, but never at the expense of truth:

“There can at the same time by no doubt that the Holy Ghost is to be viewed as commending in this passage that mutual harmony which should subsist amongst all God’s children, and exhorting us to make every endeavor to maintain it.  So long as animosities divide us, and heart-burnings prevail amongst us, we may be brethren no doubt still by common relation to God, but cannot be judged one so long as we present the appearance of a broken and dismembered body.  As we are one in God the Father, and in Christ, the union must be ratified amongst us by reciprocal harmony and fraternal love. . .We are to set ourselves against those turbulent spirits which the devil will never fail to raise up in the Church, and be sedulous to retain intercourse with such as show a docile and tractable disposition.  But we cannot extend this intercourse to those who obstinately persist in error, since the condition of receiving them as brethren would be our renouncing him who is Father of all, and from whom all spiritual relationship takes its rise.  The peace which David recommends is such as being in the true head, and this is quite enough to refute the unfounded charge of schism and divisions which has been brought against us by the Papists, while we have given abundant evidence of our desire that they would coalesce with us in God’s truth, which is the only bond of holy union.”

John Calvin, Commentary on the Book of Psalms, 5 vols. Grand Rapids: Baker, 1979, 1:189