Metropolitan Housing Project

The unchangeable part of the liturgy or the "essential component":

In every liturgy there is an "essential component": without it, the liturgy is no longer possible. For example, in the Mass, the "essential component" consists of

• the offering of bread and wine,

• the Consecration,

• Communion.

If one of these elements is missing, there is no celebration of the Eucharist; there is nothing left but a simulation of the Mass.

The parts subject to change include

The "substantial" components:

Every liturgy includes a "substantial" part, which, in itself, is not necessary for the Eucharistic liturgy but which is found in more or less developed forms in all the Christian liturgies.

This part is made up of psalms (entrance antiphon, gradual or responsorial psalm, Communion antiphon) as well as readings from Sacred Scripture (Old Testament, Letters of the Apostles, Gospel). It also includes the use of incense, the vestments, posture, and gestures of the officiating ministers, the different prayers, and so forth.

The "modal" component:

This comprises the manner in which the "essential" and "substantial" components take place or are supposed to be carried out.

The "modal" component depends to a great extent on the traditions of the local churches. It determines the order of the ceremonies and thus allows us to distinguish between large fan-lilies of rites (the Roman rite, the Ambrosian rite, the rite of Lyons, the Maronite rite, the rite of Saint John Chrysostom, etc.).

The "accessory" components:

Unlike the essential and substantial parts of the liturgy, the "accessory" component is not codified: it does not immediately concern the beliefs of the faithful and can therefore be left to the discretion of those who are responsible for conducting the liturgy.

The "accessory" component is used to enhance the elements of the three other components of the liturgy; it appeals to "good taste" and to "common sense" and thus includes everything that...