Purgatory belongs to the Catholic faith. However, aspects of it can be found in other cultures and religions, which affirm that purification is necessary after death. Explanations from don Paul Denizot interviewed by Guillaume Desanges for RCF in Chroniques du purgatoire #3.
Purgatory as old as time
Two aspects of purgatory are to be found in a common fund of humanity. First, there’s the question of purification, which is necessary to achieve completion and fulfillment. This is the case in the successive reincarnations of Hinduism. They are a form of purification. This is also the case in the rites of passage of the deceased in Egypt, or of the Greek who must give a coin to cross the River Styx.
The living in solidarity with the dead
Secondly, the question of prayer for the departed is found in humanity in general, with prayer or rites practiced to help the deceased gain access to an afterlife. This means that the living are aware that they can help the deceased, and that there is something after death.
The idea of purification after death
Even people with no religion have this idea of purification with the aim of becoming better, good or truly themselves. That’s why the personal development sections in bookshops work so well. The difficulty is that you can’t do it on your own. Trying to do it alone is often a dead end.