Gregorian Masses consist of 30 holy Masses said in succession and without interruption for the deliverance of an individual soul from Purgatory to heaven.
According to legend, dating back to mid-sixth century, a deceased monk appeared and requested 30 Masses to be celebrated for the release of his soul from Purgatory. On completion of the stipulated number of days, he appeared once more radiant in heavenly glory.
These 30 Masses are called Gregorian Masses because Saint Gregory contributed to the spread of this pious practice. Saint Gregory, as we read of his life, was also instructed by God Himself in the efficacy of these 30 Masses and he recommended the practice on various occasions.
Pope Benedict XIII lauded this pious practice of having thirty Masses said for each departed soul.
In Italy, France, Spain, Germany and especially England, which was converted by missionaries sent by Saint Gregory, it was an established custom prior to the Reformation and the French Revolution. In a number of old churches in Europe, altars dedicated to St. Gregory and the Poor Souls are to be found. Many old paintings are still preserved attesting the same fact.
Several Religious Orders have it specified in their rules and Constitutions that 30 Gregorian Masses are to be said for every deceased member. The Franciscans, Dominicans, Salesians of Don Bosco, Capuchins and others carry on this practice.
HOW TO ARRANGE GREGORIAN MASSES
There is no need to follow special instructions to arrange Catholic Masses for the dead. You can do so with any priest who is willing or able to say them for you for a soul nominated by you. However, we find the Salesians of Don Bosco to be the most reliable and affordable source.