Since it’s been mentioned over and over again, I won’t touch on where in the Bible Purgatory is described and validated, but recommend some reading:
A good modern book is called Hungry Souls, it’s about apparitions and private revelations concerning Purgatory, and it very nicely explains it as a doctrine, a process, and a place. Another good one is much older, called simply Purgatory, I think by a woman named Sinclair, written in 1884, available as an e-book for Kindle for free. (If you don’t have a Kindle, you can download Kindle for PC for free.) This e-book is a conglomeration of many sources on the topic, including writings of the early Church Fathers and saints who have had special knowledge given them (Catherine of Siena for example). If I remember correctly, the e-book has an imprimatur, I don’t recall about Hungry Souls. But since my opinion means so much, it has my imprimatur–I didn’t see anything contrary to faith in either book.
My understanding is that Purgatory is a place in the same sense that Heaven and Hell are places, and what the soul undergoes there is both purification and punishment. A soul is rightfully (and willingly) punished for unconfessed sins, and made pure from the stain of sins committed and forgiven. I’ve heard the analogy of breaking a neighbor’s window–the neighbor forgives you, but you still have to pay for a new window. However in this life we may be grumpy about paying for the window, after death we are given a glimpse at our personal judgment of the glory of God which we will (or will not, if hellbound) attain after purification. We see, if only briefly, the perfection and holiness of God, are given to understand the gravity of our sins and how not even the least smear of the stain of sin can enter into His presence, and willingly are sent to Purgatory to have the offenses burned away. There is a parable in the Bible (sorry I don’t have the verse offhand but I’m sure it’s been quoted already) about how the fire destroys all a man’s works, whether they be gold or dross, until the man emerges. Our sins are taken into account, but so are our virtues, which are like the man’s gold. The hay (sin) burns away to nothing, leaving a man and his refined gold, which survived the fire.
The soul knows its sinfulness, and wishes to be purified so it can enter into the presence of God. Given the choice, the soul would not go to God before undergoing purification, understanding this to be insult and blasphemy. There are two forms of suffering for the soul in Purgatory–pain of sense and pain of loss. Pain of sense is what we’d understand as physical torment, of the body (although the soul is separated from the body, the soul comprehends pain), caused by (depending on the source) fire or ice (some revelations of Purgatory are of a frozen lake, or even of being alternated between fire and the frozen lake). The suffering has been compared to the severity of torment to a soul in hell (beyond any earthly, bodily pain), with the exception that in hell there is no hope of it ever ending. In Purgatory, one suffers with the knowledge that it is for his perfection and that he will, someday, be released to go to God. Pain of loss is the suffering caused by knowing the beauty of God, and having to exist (for a time) away from it. The soul has seen God and longs for Him, the longing growing more painful the closer to holiness the soul becomes.
The image of concentric circles or a spiral is used in Hungry Souls, like planets orbiting around the sun: each planet in this case is a soul, and God is the sun. The souls farthest from God and with the most stain of past sins are cold and may not feel a strong pain of loss because they don’t so much care they are far from God. But as they attain holiness and atone for their sins, they circle slowly closer to the center, where they gain warmth and become more aware of their longing to be with God, rather than kept away from Him.
Pain of sense apparently can be relieved by the prayers and suffering of the living–which is why in all the apparitions from Purgatory, they always ask for Masses and prayers to ease their suffering. This is what we can do to help, for they are not allowed to pray for themselves. They are allowed to pray and intercede for us (and indeed will remember us when we have died–there are revelations as well of the souls released from Purgatory by a saint assisting that saint directly into Heaven), but not for themselves. God has willed that their only hope for prayer come from the living. So we can and should relieve their suffering here on Earth (and preemptively devote our sufferings to ease our pain in Purgatory for our perfection) as a work of mercy and love. When that debt has been paid, they may still have a time in Purgatory for the complete perfection of their soul because of the pain of loss. This we cannot really ease, they have to wait it out, but can do so without the torments of the pain of sense, and they are willing to wait this time and suffer the separation from God, because they are fully understanding and accepting of His will.
So the takeaway: Purgatory is purification and punishment, but undertaken willingly by the soul, because of the knowledge that eventually it will be united with God again. We must pray for them because they cannot pray for themselves, but in their gratitude, will pray for us.
I have read your posts through slowly a second time and think I understand your position well. I will try to type something up, and may submit it as a seperate thread. Keep your eyes open for it but I do have to work today so may not get to it for a while.