Philip of Hesse brought the leaders of the two Reformations together at Marburg in October 1529 for a plainly political purpose: a united Protestant front needed a united Protestant theology. The colloquy produced agreement on fourteen of fifteen articles. The fifteenth concerned the Lord's Supper, and it did not move.
Luther wrote the words hoc est corpus meum on the table in chalk and refused to be argued off them. His position rested on two commitments. The first was hermeneutical: the words of institution mean what they say unless Scripture itself indicates otherwise, and he regarded Zwingli's reading of is as signifies as the kind of manoeuvre that could empty any text. The second was christological: since the divine and human natures in Christ are united, the properties of the divine nature communicate to the human, and Christ's body can therefore be present wherever he wills, not confined to one location in heaven.
Zwingli held that a body is by definition in one place, that Christ's body is at the right hand of the Father, and that the sacrament is a memorial and a public pledge of allegiance among believers. He read the sixth chapter of John, where Jesus says the flesh profits nothing, as decisive against a bodily eating.
Neither man conceded. Luther is reported to have told the Swiss that they had a different spirit. The Marburg Articles recorded agreement on almost everything and registered the disagreement on this, and the Reformation entered its second decade permanently divided into Lutheran and Reformed camps, with political and military consequences across the following century.