Luther and Zwingli Had to Admit Mary's Perpetual Virginity Before the Marburg Colloquy?

The following comment was left on a previous blog entry:

James,Could you help me find a quote online that I am quite sure I read in a book about 30 years ago? At the Marburg Cooloquy where Luther and Zwingli argued about the Real Presence, before the fireworks began, both men had to prove they had an orthodox understanding of scripture by agreeing that Mary was a Perpetual Virgin despite the term "brother". I may not have it 100% correct but I think I am close. I have googled for it but to no avail. Are you familiar with this? Could you post it or email it? Thanks.

I don't recall ever hearing this before, but it sounded intriguing enough to look into. My suspicion is that the thirty-year old memory may refer to something from The Marburg Colloquy and the Marburg Articles (1529) [LW 38:3]. Luther came face to face with Zwingli in 1529 at Marburg.

In one of the reports of this meeting, a dialog between Oecolmapadius and Luther on the Lord's Supper is described. Oecolmapadius argues for a metaphorical interpretation of "This is my body," while Luther argues for a literal interpretation.  And then:

Zwingli begins to accuse Luther of prejudice because he [Luther] testifies that he is unwilling to abandon his view. In the same way Helvidius, with reference to the word “brother,” could prove [that Jesus had brothers], since it is clearly written “his brothers” [John 7:3]. We should compare one passage of Scripture with another. Therefore, if we do not have a passage which says, “This is the figure of my body,” we nevertheless have a passage which leads us away from bodily eating. For that reason [it follows] he did not give his body physically in the Supper. (LW 38:54)

Luther proves from Scripture against Helvidius that the word “brother” can be used for “cousin.” But it cannot be proved that “This is my body” is a trope. If God told me to eat a crabapple, I would eat spiritually. For wherever the word of God is, there is spiritual eating. Therefore, since he added the bodily eating by saying, “This is my body,” it is to be believed. By faith we eat this body which is given for us. The mouth receives the body of Christ, the soul believes the words that it is eating the body. (LW 38:55)

Here is another description:

Zwingli: It is prejudice if he does not want to give up his opinion. He is not willing to give it up unless a passage is cited which proves that “body” means “figure of my body.” This is the prejudice of heretics, for example, of Helvidius who denied that Jesus was the only son of Mary, because it cannot be proved from Scripture. It is necessary to compare one Scripture passage with another. Even if we do not have [a passage that says], “This is the figure of my body,” we do have [a passage] which leads us away from the bodily eating. It is the purpose of our meeting here to look at the passages, and we ought to consider the passage [in John 6] because it leads away from bodily eating. Hence it follows that in the Supper Christ did not give himself in bodily fashion. (LW 38:20)

Luther promised that they would lay aside all passions for the sake of God and the prince. What is lost, is lost. Let us hope for the future. Even if they cannot agree on everything, they might discuss at the close of the colloquy whether or not they can regard each other as brethren.—As to the argument of Helvidius: It can be proved from Scripture that the word “brother” may be used for “cousin.” But it cannot be proved that “This is my body” is a trope. What you call eating may do away with all eating; “flesh, flesh” means eating according to you. Form your own opinion, this has nothing to do with the matter itself; I would eat rotten apples or dried-up pears if God would place them before me. Where the word of God is, there is spiritual eating. Whenever God speaks to us, faith is required, and such faith means “eating.” If, however, he adds bodily eating, we are bound to obey. In faith we eat this body which is given for us. The mouth receives the body of Christ, the soul believes the words when eating the body. If I receive the body of Christ into my arms, this would be for the purpose of embracing it. You have your interpretation and mean well; but this is of no consequence. Furthermore, when you say that God does not propose to us anything incomprehensible, I could not admit this. [Consider] the virginity of Mary, the forgiveness of sins, and many similar matters. So also, “This is my body” [is incomprehensible]. “Thy path was through the great waters, yet thy footprints were unseen” [Psalm 77:19]. If we knew his ways, he who is marvelous would not be incomprehensible. (LW 38:21-22)