Requirements for the celebration of Gregorian Masses were gathered from the following questions put to the Sacred Congregation of Indulgences regarding the celebration of Gregorian Masses and the answers given to them. (March 15, 1884; August 24, 1888; January 14, 1889. Also Benedict XIV, inst. 34, No. 22).
Q. Must the 30 Masses called Gregorian be said by the same priest?
A. There is no obligation for them to be said by the same priest.
Q. Must they be said for one soul alone, without any other intention?
A. Yes, the Masses should be said exclusively for the soul whose deliverance from the pains of Purgatory is especially solicited from the Divine Mercy.
Q. Should they be said on thirty consecutive days without interruption?
A. Yes, for thirty days without interruption.
Q. What is the difference between a funeral Mass and a Memorial Mass?
A. A Funeral Mass, requires a body to be present, and occurs soon after one’s death. A Memorial Mass is offered in the memory of a deceased person near or any time after death.
Q. If the Gregorian Masses fall in the course of the Triduum does it constitute an interruption?
A. It does not, provided the celebration of the thirty Masses be resumed on Easter Sunday.
Q. Do they need to be said on the same altar?
A. Not necessarily. They may be said on different altars.
Q. Must the Requiem Mass be said, at least when the Rubric permits it?
A. Although it would seem proper, it is not an essential condition. The obligation is satisfied by saying the Mass of the day.
Q. May the Gregorian Masses be offered for the living?
A. No, they cannot be said for the living, as they are intended exclusively for departed souls.