Today the Church celebrates the Commemoration of All the Faithful Departed, commonly referred to as All Souls Day. Once again, I’d like to turn to the Daily Roman Missal for a great explanation of this celebration:
The Church, after celebrating the feast of All Saints, today prays for all who, in the purifying suffering of purgatory, await the day when they will join in their company. The celebration of the Mass, which re-enacts the sacrifice of Calvary, has always been the principal means by which the Church fulfills the great commandment of charity toward the dead. We can also relieve their sufferings through our prayers, suffrages and penances. Even after death, links with our fellow travelers are not broken.
Today, in addition to praying for the souls of all our deceased relatives and friends, we should pray for those souls who have no one to pray for them. This includes the souls of just about all non-Catholic Christians, as most of their denominations don’t believe in the practice of praying for the deceased.