An ancient but mostly unknown custom of the Church is the offering of a daily Mass for 30 days for a soul in Purgatory. After the Masses are said, the soul would immediately be freed from Purgatory and enter Heaven.
As its name implies, Gregorian Masses were named after St. Gregory the Great who was the pope from 590 to 604 A.D. This traditional sequence of Masses was not started by St. Gregory but became popular when he promoted it.
In his Dialogues, St. Gregory wrote that he had one Mass said each day over 30 days for the soul of Justus (a monk who had recently died). After the last Mass was said for him, he appeared to his brother, Copiosus, to tell him the good news of his departure from Purgatory into Heaven. Copiosus did not know about the 30 Masses that were said for his brother. He found out about them later when he spoke to the monks about his brother’s deliverance.
In the church of Sts. Andrew and Gregory (located on Mt. Coelius, where Justus had died in the convent of St. Andrew), there is an inscription of a private revelation that St. Gregory received on the benefits of 30 consecutive Masses for a soul in Purgatory.
It is not known why Gregorian Masses would release a soul from Purgatory. The custom of praying 30 days for the dead can be traced back to the Old Testament. The Jews prayed for 30 days after the death of Moses according to their “days of weeping for the mourning rites” (Deuteronomy 34:8).
Gregorian Masses spread throughout Europe and many Religious Orders. It unfortunately faded after the Protestant Reformation and the French Revolution, but the love Catholics have for the holy souls gradually brought back this practice.
The 30 Masses must be said one day after another without any interruption. The way the Masses are to be said is once per day for 30 consecutive days. They can only be said for one person at a time who is in Purgatory. If the blessed soul is already in Heaven, the indulgences may be applied to another needy soul according to God’s infinite mercy.
The Masses must be said one day after another without any interruption. The exception to this is if the last three days of Holy Week occur during the Gregorian Masses. If this is the case, then the Masses may be stopped until Easter Sunday and then continued on that day. The 30 Masses cannot all be Masses of Requiem. They can also be said at any altar.
A problem that might arise is that most parish priests will not have the time to do a daily Mass for an individual in Purgatory. A solution to this is to find a priest who is retired or contact a monastery where you can usually find priests and monks available for Gregorian Masses.
If Gregorian Masses can be done then it is a great blessing for a soul in Purgatory. If the cost is too high, there are other effective ways to free souls from Purgatory, such as praying for them in Masses, rosaries, novenas, charitable works, etc. Gregorian Masses are but one option we Catholics have to help those in Purgatory. (From Holy Souls Online)