All Souls Day is a solemn day in the Catholic Church dedicated to praying for all the faithful departed. This includes those who have died and are believed to be in Purgatory, undergoing purification before entering heaven.
The Church teaches that the prayers, Masses, and sacrifices offered by the living can help these souls in their journey towards the fullness of God’s presence. This day emphasizes the interconnectedness of the Church triumphant (those in heaven), the Church militant or pilgrim church (those on earth), and the Church suffering (those in purgatory).
A plenary indulgence, applicable only to the souls in Purgatory, is granted to any of the faithful who 1) On one of the days from 1 to 8 November visit devoutly a cemetery or who simply pray mentally for the dead; 2) On All Souls Day (or else with the permission of the Ordinary, on the Sunday that precedes or follows, or else on All Saints’ Day) visit a church or chapel with devotion and there recite the Our Father and the Creed.
A partial indulgence, applicable only to the souls in Purgatory, is granted to any of the faithful who 1) Visit devoutly a cemetery or who simply pray mentally for the dead; 2) Recite devoutly Lauds or Vespers of the Office of the Dead, or the invocation Eternal rest grant… (Enchiridion of Indulgences, edition of 1999, concession 29)