All Souls Day is often overshadowed by the two days preceding it, All Hallow's Eve (Halloween) and All Saints Day (November 1). All Hallows (Holy) Eve and All Saints Day are the times we remember all of the Saints who have gone before us in faith and we now know to be in Heaven, especially those who are the lesser-known saints. All Souls Day is a solemn celebration in the Roman Catholic Church commemorating all of those who have died and now are in Purgatory (those who we don't know for sure have made it to heaven), being cleansed of their venial sin's and the temporal punishments for the mortal sins that they have confessed and atoned before entering fully into Heaven.
History of All Souls Day
The importance of All Souls Day was made clear by Pope Benedict XV (1914-22), when he granted all priests the privilege of celebrating three Masses on All Souls Day: one for the faithful departed; one for the priest's intentions; and one for the intentions of the Holy Father. Only on a handful of other very important feast days are priests allowed to celebrate more than two Masses.
While All Souls Day is now paired with All Saints Day, which celebrates all of the faithful who are in Heaven, it originally was celebrated in the Easter season, around Pentecost Sunday (and still is in the eastern Catholic Churches). By the 10th century, the celebration had been moved to October, and sometime between 998 and 1030, Saint Odilo of Cluny decreed that it should be celebrated on November 2 in all of the Benedictine monastery's.
Over the next two centuries, other Benedictines and the Carthusian's began to celebrate it in their monasteries as well, and soon it spread to the entire church.
On All Souls Day, we not only remember the dead, but we apply our efforts, through prayer, almsgiving, and the Mass, to their release from Purgatory. There are two plenary indulgences attached to All Souls Day, one for visiting a church and another for visiting a cemetery. (The plenary indulgence for visiting the cemetery can also be obtained every day from November 1–8, and, as a partial indulgence, on any day of the year.) while the actions are performed by the living, the merits of the indulgences are applicable only to the souls in Purgatory.
Praying for the dead is a Christian obligation. In the modern world, when many have come to doubt the church's teaching on Purgatory, the need for such prayers has only increased. The church devotes the month of November to prayer for the Holy Souls in Purgatory, and participation in the Mass of All Souls Day is a good way to begin the month.