The Commemoration of the Faithful Departed extends the All Saints' celebration to the whole company of the baptized dead — not only the recognized saints but all who have died in the faith and whose purification may not yet be complete. The day expresses the ancient Christian practice of praying for the dead, attested from the earliest centuries and grounded in the conviction that the bond of love in Christ survives death.

The theological tradition around prayer for the dead is one of the areas where Western Christianity developed differently from the East, and where the Reformation created further divergence. The Catholic doctrine of purgatory, formalized at the Councils of Florence (1439) and Trent (1563), holds that the faithful who die with unconfessed venial sins undergo purification before entering heaven, and that the prayers of the living can assist them. The Orthodox tradition affirms a state of purification but rejects the juridical language of 'satisfaction.' The Anglican tradition, as expressed in the Articles of Religion (XXII), rejected 'the Romish doctrine concerning Purgatory' while not categorically forbidding prayer for the dead — and Anglican practice has retained it, particularly in Anglo-Catholic usage. The BCP 2019 includes this commemoration, reflecting ACNA's willingness to practice prayer for the dead within a Reformed Catholic framework.

The practice of praying for the dead is ancient. The Jewish precedent is 2 Maccabees 12:39-45, where Judas Maccabeus makes atonement for fallen soldiers. Early Christian writers attest the practice: Tertullian (c. 200) mentions annual commemorations of the dead; Cyprian (d. 258) references prayer for the departed; Augustine (d. 430) discusses the benefit of prayer for the dead at length in the Enchiridion and City of God.

The formal institution of November 2 as a commemorative day is attributed to Odilo, Abbot of Cluny, in 998. He directed all Cluniac monasteries to observe the day after All Saints as a day of prayer for the faithful departed. From Cluny, the practice spread through the Benedictine network — the Diocese of Liège adopted it around 1008 — and became universal in the Western Church by the twelfth-thirteenth centuries.

The Eastern Orthodox equivalent is the system of Soul Saturdays (Psychosabbata), distributed throughout the liturgical year rather than concentrated on a single date. The theological differences are significant: Catholicism developed the doctrine of purgatory; Orthodoxy speaks of purification without the juridical framework; Anglicanism affirms prayer for the dead while remaining agnostic about the mechanism of post-mortem purification.

• Commemorated