In a brief 1949 article in the Lutheran Quarterly, Roland Bainton observes that, far from being stubborn and intransigent at the 1529 Colloquy at Marburg, Luther and the Lutherans “took the initiative in proposing a formula of concord. They confessed that the discussion had opened their eyes and they were prepared to repudiate all of their previous works against Zwingli and Oekolampadius as irrelevant because based on misunderstanding. Zwingli as a matter of fact had advanced from the view that the Lord's Supper is only a memorial to the position that Christ is spiritually present. Luther had always insisted that whatever the nature of the physical presence, it is of no benefit without faith. Hence any magical view of the sacrament is excluded” (396).
This led the Lutherans to formulate a consensus statement “that Christ is truly present, that is substantively (they did not say substantially), essentially though not quantitatively, qualitatively or locally.” Bainton writes that “the Swiss rejected this statement as not sufficiently safeguarding the spiritual presence, and also because they could not understand how anything could be present somewhere without being there locally. They were not satisfied by Luther's explanation that the categories of geography do not apply to the presence of God. Agreement had failed” (396).
On the suggestion of Philip of Hesse, Luther momentarily agreed that, despite the divergence in theology, the Swiss and Germans should maintain intercommunion, only to be dissuaded when Melanchthon warned him about the consequences of such an agreement. Luther backed away “out of consideration for Ferdinand and the Emperor” (396–7).
Martin Bucer, who was present and reported this moment in a letter, “implied that the motives of Melanchthon were political, that he was endeavoring to secure toleration by disclaiming the more radical co-believers.” Bainton thinks that unfair. Rather, Melanthchon “still entertained a hope of reunion with Rome and he did his best the following year at Augsburg to achieve it. Then the roles of Melanchthon and Luther were reversed. At Marburg Luther wanted to yield to the Swiss but Melanchthon would have none of it. At Augsburg Melanchthon was on the point of yielding to the Catholics, but Luther would have none of it” (397).
As Bainton says, the remarkable thing about Bucer's report is “Luther's momentary readiness to sanction communion other than on the basis of doctrinal unanimity. He was there endorsing the Anglican principle that men may join in a common act of worship even though they may place upon it different constructions” (398).
(Bainton, “Luther and the Via Media at the Marburg Colloquy,” LQ 1949: 394–8.)