2. As for any admonitions issued before the readings, these must be brief. Adherence must also be shown to what is set out in the “Institutio Generalis Missalis Romani” (nn. 105 and 128) and to the Praenotanda of the “Ordo Lectionum Missae” (nn. 15, 19, 38, 42).
3. The homily, because of its nature and importance, is reserved to the priest or deacon (cf. Codex Iuris Canonici, can. 767 § 1). As for the occasional contribution of testimonies on the part of the lay faithful, the proper places and methods for these are indicated in the Interdicasterial Instruction “Ecclesiae de Mysterio,” which was approved “in specific form” by Pope John Paul II and published on August 15, 1997. In this document, sections 2 and 3 of article 3 read as follows:
§2 - “It is permitted to have a brief instruction that helps explain better the liturgy that is being celebrated, and even, in exceptional circumstances, a few testimonies, as long as these conform to the liturgical norms, are offered on the occasion of Eucharistic liturgies celebrated on particular days (for seminarians, the sick, etc.), and are thought truly helpful as an illustration of the regular homily delivered by the celebrating priest. These instructions and testimonies must not assume characteristics that might cause them to be confused with the homily.”
§3 - “The possibility of ‘dialogue’ during the homily (cf. Directorium de Missis cum Pueris, no. 48) can be used occasionally and with prudence by the celebrating minister as a means of exposition, which does not transfer to others the duty of preaching.”
Careful attention must also be paid to the Instruction “Redemptionis Sacramentum,” no. 74.
[74.] If the need arises for the gathered faithful to be given instruction or testimony by a layperson in a Church concerning the Christian life, it is altogether preferable that this be done outside Mass. Nevertheless, for serious reasons it is permissible that this type of instruction or testimony be given after the Priest has proclaimed the Prayer after Communion. This should not become a regular practice, however. Furthermore, these instructions and testimony should not be of such a nature that they could be confused with the homily, nor is it permissible to dispense with the homily on their account.