In 1544, Heinrich Bullinger was pastoring in Zurich when he and his colleagues there fell afoul of Martin Luther—hardly the first or the last to do so. Luther had written another treatise against their view of the Lord’s Supper and had employed his too-typical fire. Bullinger wrote John Calvin in nearby Geneva to ask his counsel and Calvin responded with a letter than models respect amid disagreement.
I hear that Luther has at length broken forth in fierce invective, not so much against you as against the whole of us.
On the present occasion, I dare scarce venture to ask you to keep silence, because it is neither just that innocent persons should thus be harassed, nor that they should be denied the opportunity of clearing themselves; neither, on the other hand, is it easy to determine whether it would be prudent for them to do so. But of this I do earnestly desire to put you in mind, in the first place, that you would consider how eminent a man Luther is, and the excellent endowments wherewith he is gifted, with what strength of mind and resolute constancy, with how great skill, with what efficiency and power of doctrinal statement, he had hitherto devoted his whole energy to overthrow the reign of Antichrist, and at the same time to diffuse far and near the doctrine of salvation. Often have I been wont to declare, that even although he were to call me a devil, I should still not the less hold him in such honour that I must acknowledge him to be an illustrious servant of God.
But while he is endued with rare and excellent virtues, he labours at the same time under serious faults. Would that he had rather studied to curb this restless, uneasy temperament which is so apt to boil over in every direction. I wish, moreover, that he had always bestowed the fruits of that vehemence of natural temperament upon the enemies of the truth, and that he had not flash his lightning sometimes also upon the servants of the Lord. Would that he had been more observant and careful in the acknowledgement of his own vices.
Flatterers have done him much mischief, since he is naturally too prone to be over-indulgent to himself. It is our part, however, so to reprove whatsoever evil qualities may beset him, as that we may make some allowance for him at the same time on the score of these remarkable endowments with which he has been gifted. This, therefore, I would beseech you to consider first of all, along with your colleagues, that you have to do with a most distinguished servant of Christ, to whom we are all of us largely indebted;
Besides, you will do yourselves no good by quarreling, except that you may afford some sport to the wicked, so that they may triumph not so much over us as over the Evangel. If they see us rending each other asunder, they then give full credit to what we say, but when with one consent and with one voice we preach Christ, they avail themselves unwarrantably of our inherent weakness to cast reproach upon our faith. I wish, therefore, that you would consider and reflect on these things rather than on what Luther has deserved by his violence, lest that happen to you which Paul threatens, that by biting and devouring one another, ye be consumed one of another. Even should he have provoked us, we ought rather to decline the contest, than to increase the wound by the general shipwreck of the Church.
(Thanks to W. Travis McMaken for the context and partial transcription from John Calvin: Tracts and Letters)