Under another entry I posted an email from a priest about his experience of being in the congregation during the celebration of Mass according to the Novus Ordo, the Ordinary Form. HERE
This raised, again in email, questions from priests about the propriety, or liceity, of priests participating at Mass in the congregation, in the manner of the lay faithful.
There is a paragraph in the Congregation for Divine Worship’s document Redemptionis Sacramentum which deals with this.
[128.] Holy Mass and other liturgical celebrations, which are acts of Christ and of the people of God hierarchically constituted, are ordered in such a way that the sacred ministers and the lay faithful manifestly take part in them each according to his own condition. It is preferable therefore that “Priests who are present at a Eucharistic Celebration, unless excused for a good reason, should as a rule exercise the office proper to their Order and thus take part as concelebrants, wearing the sacred vestments. Otherwise, they wear their proper choir dress or a surplice over a cassock.” It is not fitting, except in rare and exceptional cases and with reasonable cause, for them to participate at Mass, as regards to externals, in the manner of the lay faithful.
First, this says “not fitting” not “not licit”.
Second, a reasonable cause can be that a) the priest is not in the state of grace, b) he already said Mass that day c) he forgot his cassock, d) he got there late, e) etc.
So, as a general and important rule, priests should not be in the congregation unless they have a reasonable cause to be.
The flip side of the coin is that lay people should not be in the sanctuary unless they have a reasonable cause to be, a role to fulfill that requires their presence.
We must avoid the “laicization” of priests and the clericalization of the laity.
St. Augustine of Hippo taught that Christ speaks in every word of the psalms. Sometimes Christ speaks at the Head, sometimes as the Body, sometimes as Head and Body together, Christus Totus. This is a useful paradigm for understand our liturgical roles and also for the design of a church building.
The priest stands in persona Christi as the Head of the Body, the Church. When the priest speaks on his own, Christ the Head is speaking. The laity have their role as the Body. When they respond, Christ the Body responds. At times priest and people speak together.
The sanctuary is where the Head is found. The nave is where the Body is found. There is a meeting point where Communion is distributed and received. The presence of a Communion rail helps to underscore this theological point: it brings special attention to that place where the Head and Body are in closest union.
But I digress….
In general, priests should not be in the congregation, particularly if they are in clerical clothing. Sometimes it happens and, when it does, the world doesn’t crumble.