General Instruction of the Roman Missal: Chapter III, The Duties and Ministries in the Mass
III. Particular Ministries
The Ministry of the Instituted Acolyte and Lector
98The acolyte is instituted to serve at the altar and to assist the priest and deacon. In particular, it is his responsibility to prepare the altar and the sacred vessels and, if it is necessary, as an extraordinary minister, to distribute the Eucharist to the faithful.[84]
In the ministry of the altar, the acolyte has his own functions (cf. nos. 187-193), which he must perform personally.
99The lector is instituted to proclaim the readings from Sacred Scripture, with the exception of the Gospel. He may also announce the intentions for the Prayer of the Faithful and, in the absence of a psalmist, proclaim the Psalm between the readings.
In the Eucharistic Celebration, the lector has his own proper office (cf. nos. 194-198), which he must exercise personally.
Other Ministries
100In the absence of an instituted acolyte, lay ministers may be deputed to serve at the altar and assist the priest and the deacon; they may carry the cross, the candles, the thurible, the bread, the wine, and the water, and they may also be deputed to distribute Holy Communion as extraordinary ministers.[85]
101In the absence of an instituted lector, other laypersons may be commissioned to proclaim the readings from Sacred Scripture. They should be truly suited to perform this function and should receive careful preparation, so that the faithful by listening to the readings from the sacred texts may develop in their hearts a warm and living love for Sacred Scripture.[86]
102The psalmist’s role is to sing the Psalm or other biblical canticle that comes between the readings. To fulfill this function correctly, it is necessary that the psalmist have the ability for singing and a facility in correct pronunciation and diction.
103Among the faithful, the schola cantorum or choir exercises its own liturgical function, ensuring that the parts proper to it, in keeping with the different types of chants, are properly carried out and fostering the active participation of the faithful through the singing.[87] What is said about the choir also applies, in accordance with the relevant norms, to other musicians, especially the organist.
104It is fitting that there be a cantor or a choir director to lead and sustain the people’s singing. When in fact there is no choir, it is up to the cantor to lead the different chants, with the people taking part.[88]
105The following also exercise a liturgical function:
The sacristan, who carefully arranges the liturgical books, the vestments, and other things necessary in the celebration of Mass.
The commentator, who provides the faithful, when appropriate, with brief explanations and commentaries with the purpose of introducing them to the celebration and preparing them to understand it better. The commentator’s remarks must be meticulously prepared and clear though brief. In performing this function the commentator stands in an appropriate place facing the faithful, but not at the ambo.
Those who take up the collection in the church.
Those who, in some places, meet the faithful at the church entrance, lead them to appropriate places, and direct processions.
106It is appropriate, at least in cathedrals and in larger churches, to have some competent minister, that is to say a master of ceremonies, to oversee the proper planning of sacred actions and their being carried out by the sacred ministers and the lay faithful with decorum, order, and devotion.
107The liturgical duties that are not proper to the priest or the deacon and are listed in nos. 100-106 may also be entrusted by a liturgical blessing or a temporary deputation to suitable lay persons chosen by the pastor or rector of the church.[89] All should observe the norms established by the Bishop for his diocese regarding the office of those who serve the priest at the altar.
IV. The Distribution of Duties and the Preparation of the Celebration
108One and the same priest celebrant must always exercise the presidential office in all of its parts, except for those parts which are proper to a Mass at which the Bishop is present (cf. no. 92).
109If there are several persons present who are able to exercise the same ministry, nothing forbids their distributing among themselves and performing different parts of the same ministry or duty. For example, one deacon may be assigned to take the sung parts, another to serve at the altar; if there are several readings, it is well to distribute them among a number of lectors. The same applies for the other ministries. But it is not at all appropriate that several persons divide a single element of the celebration among themselves, e.g., that the same reading be proclaimed by two lectors, one after the other, except as far as the Passion of the Lord is concerned.
110If only one minister is present at a Mass with a congregation, that minister may exercise several different duties.
111Among all who are involved with regard to the rites, pastoral aspects, and music there should be harmony and diligence in the effective preparation of each liturgical celebration in accord with the Missal and other liturgical books. This should take place under the direction of the rector of the church and after the consultation with the faithful about things that directly pertain to them. The priest who presides at the celebration, however, always retains the right of arranging those things that are his own responsibility.[90]