Martin Luther is perhaps the most famous and popularly respected figure of the Christian Church's Reformation, and universally remembered for hammering his theses against the church door in Wittenberg in protest against corruption.

However, Luther was constantly involved in struggles over the truth of religious doctrine, and that was every bit as true of his involvement in religious communities after they began to split from Rome as before.

In particular, when an attempt was made to unite Protestant states in the late 1520s, Luther found that he had one major sticking point: transubstantiation. That is, the belief that at the Eucharist the bread and wine literally becomes the flesh and blood of Jesus as it is consumed, as the Messiah appeared to indicate. "This is my body…."

Many Protestants believed that this was only metaphorically or perhaps spiritually true. But Luther felt strongly otherwise.

Martin Luther manuscript

Some of his feelings on the subject are made clear in an autograph manuscript fragment of Dass diese Wort Christi "Das ist mein Leib etce" noch fest stehen wider die Schwärmgeister (roughly: "That these words of Christ 'This is my body etc' continue to tell against the Visionaries").

Written in brown ink on the front and sides of a sheet of 205 x 155 mm, it bears at the head the number 6 in red pencil. He argues explicitly against the theologian Zwingli by name.

Luther's tussles with Zwingli are well recorded such as in the tense exchange citing Jesus's words "The flesh profiteth nothing" (John 6.63), Zwingli said, "This passage breaks your neck". "Don't be too proud," Luther retorted, "German necks don't break that easily. This is Hesse, not Switzerland."

The text is available at Piasa in Paris on April 13 listed at €20,000-25,000 ($35,600) with online bidding available.