Introduction The thema is interpreted as referred to Muhammad by following Nicholas of Lyra. Yet, on the historical reasons of the success of the Muslims it is said the historians have different opinions and then it is presented the summary provided by Tolomeo da Lucca OP in his Historia ecclesiastica, which underlines the responsibility of Heraclius (his pride and avidity) and his eccessive taxation, which was exploited by Muhammad to present himself "sub colore liberandi illas gentes" (f. q7v). First part In the polemical description of Muslims (and in particular, again on the life of Muhammad), the sermon draws on sources such as the Vincent of Beauvais's Historia scolastica and Riccoldo da Monte di Croce's Contra legem saracenorum (probably the main source). It briefly mentions also the letter of Pius II to Muhammed II, referring a story (fabula) about the angels Arotes e Marotes (f. r2v).  Second part It exalts the superiority of Christ and Christianity in comperison with Muhammad and Islam.