"De necessaria obligatione sacratissima communionis" Introduction frames the eucharist among the salvific tools provided by the divine providence, and says that having finhished to discuss about the sacrmaent of penance (again, underlining just contrition and confession, without space for satisfation), it is time to discuss about the eucharist by presenting three key points: the necessity (and so the obligation to it); the punishment for the omission; the preparation.    It annunces that only the first point will be discussed in this sermon, the others in the two following sermons.