Philip of Hesse wanted a military alliance. The emperor was Catholic, the Protestant princes and the Swiss cities were separately vulnerable, and a common front was worth more to him than a common doctrine. What stood in the way was a quarrel about the Lord's Supper that had been running in print for years, so Philip brought the principals to his castle at Marburg between the first and the fourth of October 1529 and had them work through fifteen prepared articles.
They agreed on fourteen. The Trinity, the two natures of Christ, original sin, justification by faith, the ministry of the word, baptism, good works, confession, civil authority, tradition: on all of it the Wittenberg and the Zurich parties found they could sign the same text. Luther and Melanchthon sat on one side, Zwingli and Oecolampadius on the other, with Martin Bucer of Strasbourg trying to build a bridge between them.
The fifteenth article was the Eucharist. Luther held that the words this is my body mean what they say and that Christ is bodily present in the bread and the wine; he is reported to have written the Latin of that sentence on the table in chalk and to have kept returning to it. Zwingli held that the sacrament is a memorial, and that Christ, being bodily in heaven, is present in it spiritually and by faith. Neither moved. The article was signed as a statement of what they had failed to agree, with an undertaking that each side would show Christian charity to the other so far as conscience allowed, and the alliance Philip wanted never came.