Thus he made atonement for the dead that they might be freed from this sin. (2 Maccabees 12:46)
Judas prays for some sinners who have died. If the dead were already in heaven, there would be no need for atonement. If they were in hell, atonement would be useless, since the punishment of hell is eternal. Thus the dead in question must have been in some “intermediate” place, i.e., what we call Purgatory.
“Settle with your opponent quickly while on the way to court with him. Otherwise your opponent will hand you over to the judge, and the judge will hand you over to the guard, and you will be thrown into prison. Amen, I say to you, you will not be released until you have paid the last penny.” (Matthew 5:25-26)
Here Jesus speaks of a purifying punishment that is temporary, from which we will finally be released, i.e., what we call Purgatory.
“And whoever speaks a word against the Son of Man will be forgiven; but whoever speaks against the holy Spirit will not be forgiven, either in this age or in the age to come.” (Matthew 12:32)
This implies that there are some sins that can be forgiven after death. Purification after death is what we call Purgatory.
“But if someone’s work is burned up, that one will suffer loss; the person will be saved, but only as through fire.” (1 Corinthians 3:15)
Purgatory has been described as a purifying fire.
May the Lord grant mercy to the family of Onesiphorus because he often gave me new heart and was not ashamed of my chains. But when he came to Rome, he promptly searched for me and found me. May the Lord grant him to find mercy from the Lord on that day. And you know very well the services he rendered in Ephesus. (2 Timothy 1:16-18)
Here Paul prays for his dead friend Onesiphorus. Again, if Onesiphorus were in heaven, he would not be in need of prayers, and if he were in hell, prayer would be pointless. This implies that Paul believed in Purgatory.
… nothing unclean will enter it … (Revelation 21:27)
That is, nothing unclean will enter the city of God, which is heaven. Few of us are perfectly pure or free of sin at the time of death. If there were no Purgatory, most of us would be doomed to hell. Thank God for His mercy in giving us the opportunity for final purification (what we call Purgatory)!