Both Martin Luther and John Calvin appealed to St. Augustine for many of their beliefs; yet St. Augustine taught the very same doctrine of Purgatory, long ago, that they wanted to reform: "St. Augustine also argues "that some sinners are not forgiven either in this world or in the next [Mat 12:32] would not be truly said unless there were other [sinners] who, though not forgiven in this world, are forgiven in the world to come" (City of God XXI.24). https://www.newadvent.org/cathen/12575a.htm
Purgatory is taught in the Old Testament (in the Deuterocanonical book of Maccabees, which Luther would later reject):
"[41] Then they all blessed the just judgment of the Lord, who had discovered the things that were hidden. [42] And so betaking themselves to prayers, they besought him, that the sin which had been committed might be forgotten. But the most valiant Judas exhorted the people to keep themselves from sin, forasmuch as they saw before their eyes what had happened, because of the sins of those that were slain. [43] And making a gathering, he sent twelve thousand drachms of silver to Jerusalem for sacrifice to be offered for the sins of the dead, thinking well and religiously concerning the resurrection, [44] (For if he had not hoped that they that were slain should rise again, it would have seemed superfluous and vain to pray for the dead,) [45] And because he considered that they who had fallen asleep with godliness, had great grace laid up for them. [46] It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins." (2 Macc 12:41-46)
And in the New Testament by Saint Paul the Apostle: "13 their work will be shown for what it is, because the Day will bring it to light. It will be revealed with fire, and the fire will test the quality of each person’s work. 14 If what has been built survives, the builder will receive a reward. 15 If it is burned up, the builder will suffer loss but yet will be saved—even though only as one escaping through the flames." (1 Cor 3:13-15) This passage says Good Christians will receive a reward from the Lord, when their works done with faith in Christ, endures or survives. Bad Christians will be saved only through fire. So it says: "builder will suffer loss but yet will be saved—even though only as one escaping through the flames"
Incidentally, this passage caused some Early Christians to be Universalists: they believed everyone could be "saved though fire" and that hell itself was essentially purifying and purgatorial only; St. Augustine rejected this, and said Purgatory is only for lesser or venial sins, i.e. non-mortal sins that are not "sins unto death" mentioned by St. John in 1 Jn 5. So the options are (1) everyone is saved through fire, and that is Universalism and wrong; or (2) no one is saved through fire, and then the above passage in the Bible would be wrong, which is impossible; or (3) only some are saved through fire, and that is precisely Purgatory. It is good and pious, as we learn from the Jewish Maccabees, to pray for the faithful departed.
God Bless.
Purgatory is taught in the Old Testament (in the Deuterocanonical book of Maccabees, which Luther would later reject):
"[41] Then they all blessed the just judgment of the Lord, who had discovered the things that were hidden. [42] And so betaking themselves to prayers, they besought him, that the sin which had been committed might be forgotten. But the most valiant Judas exhorted the people to keep themselves from sin, forasmuch as they saw before their eyes what had happened, because of the sins of those that were slain. [43] And making a gathering, he sent twelve thousand drachms of silver to Jerusalem for sacrifice to be offered for the sins of the dead, thinking well and religiously concerning the resurrection, [44] (For if he had not hoped that they that were slain should rise again, it would have seemed superfluous and vain to pray for the dead,) [45] And because he considered that they who had fallen asleep with godliness, had great grace laid up for them. [46] It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins." (2 Macc 12:41-46)
And in the New Testament by Saint Paul the Apostle: "13 their work will be shown for what it is, because the Day will bring it to light. It will be revealed with fire, and the fire will test the quality of each person’s work. 14 If what has been built survives, the builder will receive a reward. 15 If it is burned up, the builder will suffer loss but yet will be saved—even though only as one escaping through the flames." (1 Cor 3:13-15) This passage says Good Christians will receive a reward from the Lord, when their works done with faith in Christ, endures or survives. Bad Christians will be saved only through fire. So it says: "builder will suffer loss but yet will be saved—even though only as one escaping through the flames"
Incidentally, this passage caused some Early Christians to be Universalists: they believed everyone could be "saved though fire" and that hell itself was essentially purifying and purgatorial only; St. Augustine rejected this, and said Purgatory is only for lesser or venial sins, i.e. non-mortal sins that are not "sins unto death" mentioned by St. John in 1 Jn 5. So the options are (1) everyone is saved through fire, and that is Universalism and wrong; or (2) no one is saved through fire, and then the above passage in the Bible would be wrong, which is impossible; or (3) only some are saved through fire, and that is precisely Purgatory. It is good and pious, as we learn from the Jewish Maccabees, to pray for the faithful departed.
God Bless.