November 2 each year marks All Souls Day in the Catholic Church, dedicated to remembering those who have died. 

It comes one day after All Saints Day, which commemorates all saints, known and unknown. 

The practice of Christian prayer for their dead dates back to at least the second century, according to the Vatican's website, although the customs have changed over time. 

Initially, one would specifically pray for the dead three days after the person's burial, then on the anniversary of that individual's death. 

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"Remembering the dead on [November 2] became official in the year 998 when Abbot Odilo of Cluny (994-1048) made it obligatory in all the monasteries subject to him," said the Vatican website.

All Souls Day is the "one day every year when Catholics everywhere remember their past," Fr. Thomas Petri, president of the Dominican House of Studies in Washington, D.C., told Fox News Digital. 

"They remember the faithful who have preceded them," he continued — "their loved ones who have gone before them. And, in an act of filial love and piety, we pray for the deceased with the hope they will rest eternally with God in glory." 

"In the early 20th century, Pope Benedict XV granted permission allowing all priests to celebrate three Masses on All Souls Day," said the Vatican website. 

Typically, priests celebrate one Mass a day, the site notes.

"The liturgy proposes various Masses on this day, all of which are geared toward highlighting the Paschal Mystery, Jesus’ victory over sin and death," the same source indicates.

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Unlike All Saints Day, which is observed annually on Nov. 1, All Souls Day is not considered to be a holy day of obligation, in which Catholics are required to attend Mass, noted Catholic.org.

Still, the holiday is important to many Catholics.

Fr. Edward Looney, a priest in the diocese of Green Bay, Wisconsin, echoed the comments of Fr. Petri. 

"All Souls Day is a day when we pray for the dead. Our prayers and sacrifices aid souls in purgatory in the process of purification," he said. 

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When a person dies, their soul either goes to heaven, hell or purgatory, according to website Catholic Online.

"The intermediate option is purgatory, which is thought to be where most people, free of mortal sin, but still in a state of lesser (venial) sin, must go," the site notes.

Catholics believe that praying for the dead who are in purgatory helps them become spiritually prepared to enter heaven, the same source says.

"Purgatory is necessary so that souls can be cleansed and perfected before they enter into heaven. There is scriptural basis for this belief. The primary reference is in 2 Maccabees, 12:26 and 12:32," according to Catholic Online. 

Looney noted that "saints and mystics have seen purgatory," and that "we should not stop praying for our dead." 

"Even if it’s been years, because our prayers add to their accidental glory — according to St. Thomas Aquinas — which means they can better intercede for us," he added.

To properly commemorate All Souls Day, Looney advised that people "have Masses said. Pray at cemeteries. Pray the eternal rest prayer."