Commentator

The role of the commentator can be used for occasionally explain the meaning of the liturgy and how it is connected with our mission.

Key Insights

Mission
The Mass is closely connected to our call to mission, but this is not understood well.  The commentator role provides a sanctioned mechanism to address this problem.  The unexpected commentary will make members of the assembly take particular notice, so it can be an effective approach.
Don't Overuse It
The commentator role is disruptive to the liturgical flow, so it should be used rarely.  When using the role, explanations should be kept brief.
Prepare Well
The commentator script should be carefully prepared and practiced with the presider to be as smooth as possible.

Quotations

105. A liturgical function is also exercised by:
...
b) The commentator, who, if appropriate, provides the faithful briefly with explanations and exhortations so as to direct their attention to the celebration and ensure that they are better disposed for understanding it. The commentator’s remarks should be thoroughly prepared and notable for their restraint. In performing this function the commentator stands in a suitable place within sight of the faithful, but not at the ambo.
General Instruction on the Roman Missal
Second Vatican Council
The commentator also fulfills a genuine liturgical ministry, which consists in presenting to the assembly of the faithful, from a suitable place, relevant explanations and comments that are clear, of marked simplicity, meticulously prepared, as a rule written out, and approved beforehand by the celebrant. 
Lectionary For Mass: Introduction (#57)
[T]he Dismissal Rite at the end of Mass is supposed to send the entire congregation out into the world: "The Mass is ended.  Go in peace to love and serve the Lord."  This means we should carry out the mission of Jesus to proclaim and inaugurate the kingdom of God.  When seen through the lens of the Dismissal, the entire Mass is aimed at this sending forth, and every single person in the congregation is being sent on a mission that is truly worthy of his or her life.
Gregory F. Augustine Pierce
The Mass Is Never Ended: Rediscovering Our Mission to Transform the World
Servers, lectors, commentators, and members of the choir also exercise a genuine liturgical function. They ought, therefore, to discharge their office with the sincere piety and decorum demanded by so exalted a ministry and rightly expected of them by God's people.

Consequently they must all be deeply imbued with the spirit of the liturgy, each in his own measure, and they must be trained to perform their functions in a correct and orderly manner.
Constitution on the Sacred Liturgy
Second Vatican Council
#29

Recommended Script

Coming soon!

Books

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The Mass Is Never Ended: Rediscovering Our Mission to Transform the World
Gregory F. Augustine Pierce

The Mass of the Catholic Church provides everything we need to be happy, holy, and fulfilled in our lives: a mission worthy of our lives, a community to send us forth, and a spirituality of work. These three embody the 15 chapters of The Mass Is Never Ended, each of which closes with a short "story about" that synthesizes the topic and questions for reflection and discussion.  (Amazon)

Articles