First, the notion a 3rd state of sanctification is not new and has been recognized in the Orthodox Jewish religion and in Christianity up until recently (in Christian historic terms). It wasnt until the 1500s that purgatory was rejected namely during the protestant reformation. The name purgatory was given to this 3rd state/process, much like the word Trinity is used. Although not specifically named in the bible, its nature can be deduced from scripture. All Christians agree that unclean souls will not go to heaven, the teaching of purgatory allows us to understand the sanctification of our souls. Its fairly easy for Catholics to understand purgatory from scripture in Maccabees; however, this book is not in the protestant bible.
2 Macc 12:43-45 - the prayers for the dead help free them from sin and help them to the reward of heaven. Those in heaven have no sin, and those in hell can no longer be freed from sin. They are in purgatory.
Other references in scripture
… There is a divine purging fire that heals us
Hebrews 12:29 - For our God is a consuming fire.
Hebrews 12:6 - For whom the Lord loveth he chastiseth: and he scourgeth every son whom he receiveth.
Hebrews 12:10 - And they indeed for a few days, according to their own pleasure, instructed us: but he, for our profit, that we might receive his sanctification.
Isaiah 6:5 - And I said: Woe is me, because I have held my peace; because I am a man of unclean lips, and I dwell in the midst of a people that hath unclean lips, and I have seen with my eyes the King the Lord of hosts.
Isaiah 6:6 - And one of the seraphims flew to me, and in his hand was a live coal, which he had taken with the tongs off the altar.
Isaiah 6:7 - And he touched my mouth, and said: Behold this hath touched thy lips, and thy iniquities shall be taken away, and thy sin shall be cleansed.
Luke 12:59 "I tell you, you will not get out till you have paid the very last penny "
1Corinthians 3:15 Paul is telling us that at the day of judgement each man’s work will be tried… What happens if a man’s work fails the test? “He will be the loser;and yet he himself will be saved, though only as men are saved by passing through fire”
… Jesus also implied that sins can be forgiven in the next world.
Matthew 12:32 And whosoever shall speak a word against the Son of man, it shall be forgiven him: but he that shall speak against the Holy Ghost, it shall not be forgiven him neither in this world, nor in the world to come. Forgiveness is not necessary in heaven, and there is no forgiveness in hell showing there is another state after death.
… More direct examples of purgatory
Luke 12:47-48 - When the Master comes (at the end of time), some will receive light or heavy beatings but will live. This state is not heaven or hell, because in heaven there are no beatings, and in hell we will no longer live with the Master.
Luke 16:19-31 - In this story, we see that the dead rich man is suffering but still feels compassion for his brothers and wants to warn them of his place of suffering. But there is no suffering in heaven or compassion in hell because compassion is a grace from God and those in hell are deprived from God’s graces for all eternity. So where is the rich man? He is in purgatory.
1 Peter 3:19; 4:6 - Jesus preached to the spirits in the “prison.” These are the righteous souls being purified for the beatific vision.
This website has great content on purgatory.
www.saint-mike.org