Q. Where did the idea of Purgatory come from?
A. From Sacred Scripture and our elder brothers in Faith, the Jewish Faith. Please see my post: Where is Purgatory is Scripture? for the evidence of Purgatory in Scripture. The quotes below are from Kaddish,Religion Facts: Judaism and Judaism 101 .
Religion Facts: Judaism
Traditional Judaism includes belief in both heaven and hell, as we will see below. How is one’s destination decided? The School of Shammai offered this description:There will be three groups on the Day of Judgment: one of thoroughly righteous people, one of thoroughly wicked people and one of people in between. The first group will be immediately inscribed for everlasting life; the second group will be doomed in Gehinnom [Hell], as it says, “And many of them that sleep in the dust of the earth shall awake, some to everlasting life and some to reproaches and everlasting abhorrence” [Daniel 12:2], the third will go down to Gehinnom and squeal and rise again, as it says, “And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried. They shall call on My name and I will answer them“ [Zechariah 13:9]… [Babylonian Talmud, tractate Rosh Hashanah 16b-17a]
Judaism 101: Life, Death and Mourning
Kaddish is commonly known as a mourner’s prayer, but in fact, variations on the Kaddish prayer are routinely recited at many other times, ….
Why, then, is Kaddish recited by mourners?
After a great loss like the death of a parent, you might expect a person to lose faith in G-d, or to cry out against G-d’s injustice. Instead, Judaism requires a mourner to stand up every day, publicly (i.e., in front of a minyan, a quorum of 10 adult men), and reaffirm faith in G-d despite this loss. To do so inures to the merit of the deceased in the eyes of G-d, because the deceased must have been a very good parent to raise a child who could express such faith in the face of personal loss.
Then why is Kaddish recited for only 11 months, when the mourning period is 12 months?
According to Jewish tradition, the soul must spend some time purifying itself before it can enter the World to Come. The maximum time required for purification is 12 months, for the most evil person. To recite Kaddish for 12 months would imply that the parent was the type who needed 12 months of purification! To avoid this implication, the Sages decreed that a son should recite Kaddish for only eleven months.
Judaism 101: Olam Ha-Ba: The Afterlife
Gan Eden and Gehinnom
The place of spiritual reward for the righteous is often referred to in Hebrew as Gan Eden (GAHN ehy-DEHN) (the Garden of Eden). This is not the same place where Adam and Eve were; it is a place of spiritual perfection. Specific descriptions of it vary widely from one source to another. One source says that the peace that one feels when one experiences Shabbat properly is merely one-sixtieth of the pleasure of the afterlife. Other sources compare the bliss of the afterlife to the joy of sex or the warmth of a sunny day. Ultimately, though, the living can no more understand the nature of this place than the blind can understand color.
Only the very righteous go directly to Gan Eden. The average person descends to a place of punishment and/or purification, generally referred to as Gehinnom (guh-hee-NOHM) (in Yiddish, Gehenna), but sometimes as She’ol or by other names. According to one mystical view, every sin we commit creates an angel of destruction (a demon), and after we die we are punished by the very demons that we created. Some views see Gehinnom as one of severe punishment, a bit like the Christian Hell of fire and brimstone. Other sources merely see it as a time when we can see the actions of our lives objectively, see the harm that we have done and the opportunities we missed, and experience remorse for our actions. The period of time in Gehinnom does not exceed 12 months, and then ascends to take his place on Olam Ha-Ba.
Only the utterly wicked do not ascend at the end of this period; their souls are punished for the entire 12 months. Sources differ on what happens at the end of those 12 months: some say that the wicked soul is utterly destroyed and ceases to exist while others say that the soul continues to exist in a state of consciousness of remorse.
Jewish beliefs about the length of time do not correspond directly to Catholic beliefs but it is extremely interesting and noteworthy that the belief about the necessity of purification after death before entrance into Heaven pre-existed Christianity.