On All Souls’ Day, Roman Catholics commemorate and pray for the holy souls in Purgatory, undergoing purification of their sins before entering heaven. It is celebrated on November 2.
The theological basis for this feast is the doctrine that the souls which, on departing from the body, are not perfectly cleansed from venial sins, or have not fully atoned for past transgressions, cannot not yet attain the Beatific Vision, and that the faithful on earth can help them by prayers, alms, deeds and especially by the sacrifice of the Mass.
In the early days of Christianity the names of the departed brethren were recorded on tablets. Later, in the sixth century, the Benedictine monasteries commemorated their deceased during Pentecost. In Spain, there was such a day on Saturday before before Pentecost, at the time of St. Isidore (d. 636). In Germany there existed a ceremony of praying to the dead on 1 October. St. Odilo of Cluny (d. 1048) ordered the commemoration of all the faithful departed to he held annually in the monasteries of his congregation. From there, it spread among the other congregations of the Benedictines and among the Carthusians to various dioceses.
On this day, three requiem Masses are celebrated: one for the celebrant, one for the departed, and one for the Holy Father.
Prayer for the Poor Souls in Purgatory
V. Eternal rest grant unto them, O Lord.
R. And let the perpetual light shine upon them.
And may the souls of all the faithful departed, through the mercy of God, rest in peace. Amen.
V. Requiem aeternam dona eis, Domine.
R. Et lux perpetua luceat eis.
Fidelium animae, per misericordiam Dei, requiescant in pace. Amen.
Eternal Father, I offer Thee the most precious blood of Thy Divine Son, Jesus, in union with the Masses said throughout the world today for all the Holy Souls in Purgatory.