While the precise reason for his excommunication is not known, Yechiel himself claims that it was because Donin had become a Karaite, rejecting the authority of the Talmud along with the Rabbinic tradition of biblical exegesis.
[5] After ten years of living in excommunication, Donin was baptized into the Roman Catholic Church and joined the Franciscan Order.
Thirty-five articles against the Talmud were drawn up, which Donin charged with making virulent attacks on the Virginity of Mary and the divinity of Jesus.
The Pope was persuaded that the accusations were true and dispatched to the authorities of the Church transcripts of the charges formulated by Donin, accompanied by an order to seize all copies of the Talmud and deposit them with the Dominicans and Franciscans.
Louis IX ordered four of the most distinguished rabbis of France—Yechiel of Paris, Moses of Coucy, Judah of Melun, and Samuel ben Solomon of Château-Thierry—to answer Donin in a public debate.