Origins of Commemoration of the Faithful Departed
The commemoration of the faithful departed may be traced to the second century when Christians began the custom of praying for their departed brothers and sisters. Early liturgies and inscriptions on catacomb walls in Rome attest to such custom of prayers for the dead, even if the Church needed more time to develop a substantial theology behind the practice. However, it is clear that early Christians borrowed the custom of praying for the dead from Judaism, as indicated in 2 Maccabees 12:41-42. In the New Testament, St Paul prays for his departed friend Onesiphorus in 2 Timothy 1:16-18. Early Christian writers such as Tertullian (ca.160-220 A.D) and St. Cyprian (d. 258 A.D) testify to the regular practice of praying for the souls of the departed. Tertullian justified the practice based on custom and Tradition, and not on explicit scriptural teaching. Eventually, many writers, including St. Augustine (354-430 A.D), e.g. in Enchiridion of Faith, Hope, and Love and City of God, expounded on the concept of a purgation of sins through fire after death.
In the early days, departed Christians' names were carved on wooden, ivory or metal panels (diptychs). In the sixth century, Benedictine communities held commemorations for the departed on the feast of Pentecost. All Souls' Day became a universal festival largely because of the influence of Odilo of Cluny in AD 998, when he commanded its annual celebration in all Benedictine houses of his congregation. This soon spread to the Carthusian congregations as well. The day was celebrated on various days, including October 15th in 12th century Milan. Today all Western Catholics celebrate All Souls' Day on November 2, as do many Anglicans and Lutherans. Initially many Protestant reformers rejected All Souls' Day because of the theology behind the feast (Purgatory and prayers/masses for the dead), but the feast is now being celebrated in some Protestant communities, in many cases with some form of Catholic theology on Purgatory. There are many more articles on this topic, but I recommend the following web site article: that includes the teaching of the Catholic Church on Purgatory (§1030-1032).