The usual name of this service derives from its closing formula, “Ite, missa est” meaning, “Go, it is the dismissal.” The Mass as a liturgical service is perhaps more readily known to today’s public than the Divine Office, since it is regularly attended by the laity. It consists of two parts: the first is much like the Divine Office, in that it contains prayers and readings from the Bible (often collected in a lectionary for the Mass), such as were customary to the Jewish services from which the “liturgy of the word” derives. The second part contains the consecration of the bread and wine as the Body and Blood of Christ, according to the mandate in the Gospels, “This is my body… This is my blood… do this as a memorial of me” (Mark 14:22-25; 1 Cor. 11:23-25). The two parts were already fused into a single service by the middle of the second century, as shown by the writings of Justin Martyr, although the core of the second and specifically Christian part of the Mass, called the Canon, only achieved its completed form during the sixth century.
The Canon is the central section of the Mass, called by this name to indicate its “canonical” or fixed nature, in that its arrangement of prayers and rites are not subject to variations due to the seasons of the liturgical year, or to the respective rankings of any coinciding feasts. These prayers of consecration of the bread and wine are said by the priest at every Mass.
The Canon begins with the prayer, “Te igitur,” whose initial T is often hierarchically signaled by a larger size, more elaborate decoration, and sometimes a miniature. The canon may be copied in larger script for ease of reading. It may also be copied (or later, printed) on parchment, even if the rest of the book is on paper, to ensure its survival in spite of very frequent use.