Finishing Chapter V, let’s have a look at why clergy don’t just go to Mass:
[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.” [GIRM 114 cf. 16-17] 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.
A difficult omission to give or even to enforce. Sitting in a pew gives a perspective that would be invaluable to many clergy who are otherwise unaware of that perspective at Mass.