Purgatory

Purgatory is a doctrine specific to Roman Catholic Christianity (with related concepts in Eastern Orthodox and some Protestant traditions) describing a temporary post-mortem state or realm in which the souls of the righteous who died in a state of grace, but not yet fully purified of the effects of their sins, undergo a purification (purgatio) that fits them for entry into Heaven. Distinct from Hell — from which no return is possible in Catholic doctrine — Purgatory is temporary by definition: everyone who arrives eventually completes the process and moves on.

The doctrine was formally elaborated in Western Christianity during the 11th–13th centuries, drawing on earlier patristic writings and on scriptural passages (notably 2 Maccabees 12:39–46 and 1 Corinthians 3:11–15) that early theologians read as implying post-mortem purification. Dante's Purgatorio, the second book of the Divine Comedy (c. 1320), provided the definitive imaginative topography: a mountain rising from the ocean of the southern hemisphere, seven cornices around it corresponding to the seven deadly sins, with souls climbing progressively through them toward the earthly paradise at the summit and, from there, into Heaven proper. The mountain-climbing structure — that Purgatory is work, active purification, undertaken by the soul itself rather than passively endured — is one of the most theologically significant features of the doctrine.

The Eastern Orthodox and most Protestant traditions rejected the specifically Catholic formulation while preserving related concepts: Orthodox teaching describes a aerial toll-houses passage in which souls encounter and are questioned about their accumulated actions; some Protestant traditions collapse Purgatory into either Heaven or Hell; others accept a general 'intermediate state' without the elaborate Catholic doctrinal apparatus.

In broader comparative context, transitional or purification realms appear across many traditions: the Tibetan bardo through which the consciousness passes between lives; the Egyptian Duat with its weighing of the heart against the feather of Ma'at; the Islamic barzakh between death and resurrection; the various Buddhist intermediate states. These are not identical doctrines but they occupy a similar functional slot — the between-space one traverses on the way from one condition to another.

In contemporary psychedelic reports and near-death experiences, experiences of specifically purgatorial character are described: not the terror of Hell but the sustained work of confronting the accumulated shadow-material of a life, moving through it, and emerging on the other side unburdened.

Sources:
Wikipedia — Purgatory
Wikipedia — Purgatorio