Just as seating positions in the liturgy reflect the Church’s hierarchy, so does giving people particular roles.
Perhaps this part of the GIRM will help:
“294. The People of God, gathered for Mass, has a coherent and hierarchical structure, which finds its expression in the variety of ministries and the variety of actions according to the different parts of the celebration. The general ordering of the sacred building must be such that in some way it conveys the image of the gathered assembly and allows the appropriate ordering of all the participants, as well as facilitating each in the proper carrying out of his function.
The faithful and the choir should have a place that facilitates their active participation.114
The priest celebrant, the deacon, and the other ministers have places in the sanctuary. Seats for concelebrants should also be prepared there. If, however, their number is great, seats should be arranged in another part of the church, but near the altar.
All these elements, even though they must express the hierarchical structure and the diversity of ministries, should nevertheless bring about a close and coherent unity that is clearly expressive of the unity of the entire holy people. Indeed, the character and beauty of the place and all its furnishings should foster devotion and show forth the holiness of the mysteries celebrated there.”
The Instituted Acolyte, for example, has a kind of rank in the church. His leadership role is particularly evident in the absence of a priest and deacon. This is reflected in in the liturgical books:
“18. … d. An acolyte or reader who by formal institution has this special office in the Church is rightly preferred over another layperson as the minister designated at the discretion of the local Ordinary to impart certain blessings.”
(Book of Blessings, Liturgical Press, Minnesota, 1989, ISBN 0-8146-1875-8, page xxviii.)
Similarly in the document “Directory for Sunday Celebrations in the Absence of a Priest”, 2 June 1988, of the Congregation for Divine Worship, (published by USCCB, ISBN 1555862519.):
“30. In the absence of both a priest and a deacon, the pastor is to appoint laypersons, who are to be entrusted with the care of these celebrations, namely, with leading the prayers, with the ministry of the word, and with giving holy communion.
Those to be chosen first by the pastor are readers and acolytes who have been duly instituted for the service of the altar and of the word of God.”
So by having, in the liturgy, a place in the sanctuary and a particular role of reading and purifications, these ministers become known to the community. Their position in the church’s hierarchy is better understood by that community.