On the topic of Luther and Calvin, this excerpt is from the book, Portrait of Calvin by T. H. L. Parker (Philadelphia: Westminster Press, 1954). I find it quite interesting:
The original split from the Roman Church was, in face of its refusal to reform, inevitable. The divisions within the Protestant ranks, however, were a different matter. In a sense, the antagonism between Lutheran and Zwinglian was only the recognition of a fact latent from the beginning, for two strands had been present in the Reformation all along. Zwingli always insisted that he had reached his understanding of the gospel independently of Luther and at about the same time. However that may be, his outlook was very different and, as leader of the early Swiss Reformation, he impressed his outlook upon his followers. He had been profoundly influenced by the humanists and owed less to the schoolmen than did Luther; and this clean break with the immediate past gave him a far more radical attitude than Luther could stomach. Relations between them were soon strained, but they met at Marburg in 1529 in an attempt to come to terms. They agreed on everything except the Eucharist; and here both were immovable. In the end, despite their substantial agreement, the conference only served to magnify the differences and bring them into the foreground.
It is a great pity that Calvin and Luther never met, or that Calvin had not been born a few years earlier, before Luther had hardened his attitude. They were far closer to one another both theologically and in spirit than Luther and Zwingli had been. But their only real contact was through common friends. Calvin is delighted when he hears that Bucer has had a letter from Luther saying: 'Salute John Sturm and John Calvin, whose books I have read with particular pleasure', and Melanchthon tells him: 'Luther and Pomeranus have desired Calvin to be greeted; Calvin has acquired great favour in their eyes.' When some loving souls sought to stir up trouble between them by pointing out a passage in Calvin's book on the Lord's Supper where he criticizes Luther, the German Reformer said with unaccustomed gentleness: 'I hope that Calvin will one day think better of us; but in any case, it is well that even now he should have a proof of our good feeling towards him.' 'If we are not moved by such moderation, we are certainly made of stone,' says Calvin to Farel. 'For myself, I am profoundly moved by it.'
But the acquaintance made no progress into friendship; they passed only within hailing distance of each other. Four years later Calvin was still no further forward than asking Melanchthon to 'salute Doctor Martin respectfully in my name'. Luther's last years were clouded by trouble and overwork, his temper dangerous and uncertain. More and more he became inflamed against the Zurich theologians, the successors of Zwingli, who retaliated in like. Farel begged Calvin to use his moderating influence to calm down the men of Zurich. He replied that the real trouble now was Luther, whom Bullinger had borne with meekly and patiently for long. But nevertheless, he wrote to Bullinger soon after, enjoining moderation: 'I hear that Luther has at last broken out in fierce invective, not so much against you as against the whole of us.... But I do most seriously want to ask you to consider how eminent a man Luther is, and the excellent endowments he is gifted with, his strength of mind and resolute constancy, with what great skill and efficiency and power of doctrinal statement he has hitherto devoted his whole energy to overthrowing the reign of anti-Christ, and at the same time to diffusing far and near the doctrine of salvation. I have often been accustomed to declare that even though he were to call me a devil, I should none the less still 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.... Besides, you will do yourselves no good by quarrelling, but will only afford some sport to the wicked, so that they may triumph, not so much over us as over the gospel.... Even should he have provoked us, we ought to decline the contest rather than increase the harm by the general shipwreck of the Church.'
Even more important, he wrote to Luther himself a most reverent letter, calling him 'my much respected father', and sending two or three of his smaller books. Melanchthon, to whom he entrusted the letter, refused to pass it on; Luther, he said, was too suspicious of the Swiss Reformers. But there was certainly nothing in it to arouse even Luther's wrath: on the contrary, it was conciliatory in the extreme: 'Would that I might fly to you,' it concluded, 'that I might even for a few hours enjoy the happiness of your company. For I would prefer, and it would be far better, not only upon this question, but also upon others, to talk to you personally. But seeing that is not granted to us on earth, I hope that it will shortly come to pass in the kingdom of God. Adieu, most renowned sir, most distinguished minister of Christ and my ever honoured father.'
But his chief contacts with the Lutheran Church were through Melanchthon and Bucer, both his close friends. Melanchthon was, in nearly all respects, a man after Calvin's own heart. A mighty scholar-professor of Greek at Wittenberg at the age of twenty-one a humanist of wide sympathies and a Reformer who had the care of all the Churches at heart. His trouble was that, unlike Calvin, he never overcame his reserve and timidity. There was more than one complaint that he, who could write and talk so well of the Cross, had not learned to live under the Cross. And this was to be a hindrance, not only in leading to overmuch accommodation (for accommodation never yet brought about lasting union), but also in helping to prevent the important conference of all the Reformed Churches. But the friendship between him and Calvin served to bring about at least a closer understanding between the two Churches. They were to fall in the end before the obstinacy of the second generation of Lutheran theologians who, entrenching themselves firmly in Luther's theology, called Melanchthon a crypto-Calvinist and refused concessions, far less unity. After the Peace of Augsburg, when the Lutheran Church was granted the same rights as the Roman Church in Germany there was even less chance of agreement. In the future there was to be a shrewish bitterness between Lutheran and Reformed that, in earlier days, had been reserved for the common enemy, Rome.
In Switzerland, also, unity had to be fought for. There the situation was more confused than in Germany. The politically independent towns and cantons were free to choose their own religion. Part of the country clave still to the Roman Church, and even among the Reformed cities there was wide diversity; Zurich was dominated by Zwingli and afterwards by his disciple Bullinger, Berne tended to Lutheranism, and Basel, under the influence of Martin Bucer, tried to tread the slippery via media between Luther and Zwingli. What was worse, the diversities of doctrine, worship and organization were exacerbated by centuries-old feuds and jealousies between towns and families.
From the outset Calvin aimed at bringing the Swiss Churches to unity. As early as 1538 he was writing to Bullinger: 'Oh, if only a pure and sincere agreement could be reached among us at last! What then would prevent the assembling of a public synod, where individuals might propose whatever they may think to be best for the Churches? A way might be found out of going to work by common deliberation, and, if need be, that the cities and princes also should assist in this undertaking by mutual exhortation and counsel, and also confirm what is done by their authority. But in so great perplexity, the Lord is rather to be inquired of, that He Himself may open up the way.'
Little progress was made, and the Churches remained like so many stooks of corn in a harvest field before they are gathered into one rick, similar but separate. However, the leaders continued in friendliness, despite some provocation from Zurich against Bucer, generally distrusted as a mediator. Now, as later in regard to Luther, Calvin wrote to Bullinger and pleaded for moderation and a friendly spirit. When Bucer is at fault, he says, tell him so, and he will take it in the right way. But do it, not as if you were enemies, but with the love that there ought to be between fellow-ministers of Christ. And again he returns to the hope of unity: 'What, dear Bullinger, ought we rather to correspond about at this time than the preserving and confirming, by every means in our power, brotherly kindness among ourselves? We see, indeed, of how much importance it is, not only on our own account, but for the sake of the whole body of professing Christians everywhere, that all those on whom the Lord has laid any personal charge in the ordering of His Church should agree together in a sincere and cordial understanding.... Since, therefore, it is our duty carefully to cultivate friendly fellowship with all the ministers of Christ, so we must needs also endeavour by all the means we can to see that the Churches to which we faithfully minister the Word of the Lord may agree among themselves.'
Just as between Zwingli and Luther, so also between Zwingli's successors and Calvin and Bucer, it was the doctrine of the Lord's Supper that was the main point of disagreement. Bullinger was highly suspicious of Calvin as being more than half a Lutheran, and apparently nothing Calvin could say or do would make him change his mind 'a preconceived opinion of me leads you to imagine and attribute to me what never occurred to my mind'. Besides, he was a friend of Bucer's, and that in itself was sufficient to damn him. The squalid bickerings went on and on alongside the whole-hearted agreements, marring what Calvin called 'the springtime of a reviving Church'. It was not until 1549 that his patience had its reward with the union of all the Swiss Reformed Churches when they subscribed to the Consensus of Zurich which he and Bullinger had drawn up. This was a solid achievement to offset the disagreement with the Lutherans: henceforth there was one Reformed Church in Switzerland.
