Where Did the Teaching of Purgatory Originate?
Purgatory is a Catholic doctrine established at the eighth session of the Council of Florence on November 22, 1439. It was also decreed at the Council of Trent on December 4, 1563:
...the holy council commands the bishops that they strive diligently to the end that the sound doctrine of purgatory, transmitted and received by the Father and sacred councils, be believed and maintained by the faithful of Christ, and be everywhere taught and preached.i
The Catholic Encyclopedia tells us that purgatory "is a place or condition of temporal punishment for those who, departing this life in God's grace, are, not entirely free from venial faults, or have not fully paid the satisfaction due to their transgressions." ii
Catholic teaching says that purgatory is a place of purification. This cleansing occurs because salvation does not actually purify God's people enough that they can enter heaven:
All who die in God's grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death, they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven…The Church gives the name Purgatory to this final purification of the elect, which is entirely different from the punishment of the damned. iii
This doctrine is not Scriptural but instead has pagan origins. Historian Alexander Hislop tells us that every pagan system from the Egyptians to the Greeks includes a belief in purgatory. He says that "in every system, therefore, except that of the Bible, the doctrine of a purgatory after death, and prayers for the dead, has always been found to occupy a place…Paganism leaves hope after death for sinners, who, at the time their departure, were consciously unfit for the abodes of the blest. For this purpose, a middle state has been feigned, in which, by means of purgatorial pains, guilt unremoved in time may in a future world be purged away." iv Read more about purgatory and paganism from Alexander Hislop, or read our article on hell and purgatory.
The Bible says nothing about purgatory, or about the concept that our souls continue to live—in another place—immediately after we die, which is reinforced by belief in purgatory. However, it does tell us that only through Christ can we be saved; there is no other way to get to God (John 14:6). His sacrifice is enough to purify us from all our sins—big or small (1 John 1:7-9). There is no need for further purification after death. Our own works or suffering, whether here or in an afterlife, can never bring about our salvation (Ephesians 2:8-9).
Additional Sources: https://www.remnantofgod.org/Purgatory.htm