"We have no intention of yielding aught of the eternal, immutable truth of God for the sake of temporal peace, tranquility, and unity (which, moreover, is not in our power to do). Nor would such peace and unity, since it is devised against the truth and for its suppression, have any permanency. Still less are we inclined to adorn and conceal a corruption of the pure doctrine and manifest, condemned errors. But we entertain heartfelt pleasure and love for, and are on our part sincerely inclined and anxious to advance, that unity according to our utmost power, by which His glory remains to God uninjured, nothing of the divine truth of the Holy Gospel is surrendered, no room is given to the least error, poor sinners are brought to true, genuine repentance, raised up by faith, confirmed in new obedience, and thus justified and eternally saved alone through the sole merit of Christ." (Closing of Formula of Concord, Trigl. p. 1095)
Cited in Francis Pieper, The Difference Between Orthodox And Heterodox Churches, and Supplement, Coos Bay, Oregon: St. Paul's Lutheran Church, 1981, p. 65.