Tradition holds that Luther, before the debate on the Eucharist began, wrote the words hoc est corpus meum, this is my body, in chalk on the table before him, a visible reminder that he read Christ's own words at the Last Supper as literal rather than figurative and would not be argued away from that reading regardless of what philosophical or logical objections Zwingli raised. Zwingli, for his part, pointed to Christ's ascension into heaven and to other biblical language that used the same verb, is, in a plainly symbolic sense elsewhere in scripture, arguing that Luther's literalism was neither necessary nor consistent.
The failure to agree on this single article carried consequences well beyond the colloquy itself. Philip's hoped for military alliance did not come together in the form he wanted, and the Lutheran and Reformed traditions developed afterward as separate confessional families, eventually formalized in distinct confessional documents, the Lutheran Augsburg Confession and the various Reformed confessions that followed. The Eucharistic dispute opened at Marburg was never closed between the two traditions and remains one of the clearest doctrinal lines separating Lutheran from Reformed Protestantism into the present day.