A missal exists to put the whole Mass within reach of the celebrant. Its core is the Order of Mass, the fixed skeleton of the rite from the entrance to the dismissal, printed with the rubrics, the instructions traditionally set in red, that tell the priest what to do as well as what to say. Around that skeleton the book supplies the propers, the parts that change: the opening collect, the prayer over the offerings and the postcommunion for every Sunday, feast and saint's day of the year, together with the prefaces that vary the great eucharistic prayer and, in modern editions, several eucharistic prayers to choose among. Early medieval worship spread these materials across several volumes: the sacramentary held the priest's prayers, the lectionary the readings, the gradual the chants. As celebrations multiplied at side altars with a single priest taking every role, the plenary missal emerged, gathering everything into one book, and by the later Middle Ages it had become the normal form.
The modern Roman Missal reverses part of that consolidation: since the reforms of the twentieth century the readings again live in a separate lectionary, and the missal used at the altar contains the prayers and chants of the celebrant. Editions are controlled centrally, and vernacular translations are made from the Latin typical edition, so that the same book, in substance, stands on altars across the Latin Church.