Another explanation of the levels in Purgatory from this same book:
Retreat, August 1878: “Great sinners who were indifferent towards God, and religious who were not what they should have been are in the lowest stage of Purgatory. While they are there, the prayers offered up for them are not applied to them. Because they have ignored God during their life, He now in His turn leaves them abandoned in order that they may repair their neglectful and worthless lives. While on earth one truly cannot picture or imagine what God really is, but we (in Purgatory) know and understand Him for what He is, because our souls are freed from all the ties that fettered them and prevented them from realizing the holiness and majesty of God and His great mercy. We are martyrs, consumed as it were by love. An irresistible force draws us towards God who is our center, but at the same time another force thrusts us back to our place of expiation.
We are in the state of being unable to satisfy our longings. Oh, what a suffering that is, but we desire it and there is no murmuring against God here. We desire only what God wants. You on earth, however, cannot possibly understand what we have to endure. I am much relieved as I am no longer in the fire. I have now only the insatiable desire to see God, a suffering cruel enough indeed, but I feel that the end of my exile is at hand and that I am soon to leave this place where I long for God with all my heart. I know it well, I feel more at ease, but I cannot tell you the day or the hour of my release. God alone knows that. It may be that I have still many years of longing for Heaven. Continue to pray; I will repay you later on, though I do pray a great deal for you now.”
Why is it that I pray for you with less fervor than I pray for others and that often I forget to recommend you?
Do not trouble yourself about that. It is a punishment for me.
Even if you prayed more I should not be any the more relieved. God wills it thus. If He wants you to pray more He will inspire you to do so. I repeat again, do not be worried about me. You will never see me in my sufferings. Later on, when your soul is stronger, you will see souls in Purgatory and very awful ones, but let this not frighten you. God will then give you the necessary courage and all that you need to accomplish His holy will.
Is this not a punishment?
No, certainly not, I am here for my relief and for your sanctification. If you would but pay a little more attention to what I say.
That is true but these happenings are so extraordinary that I do not know what to make of them; it is not an ordinary thing to hear you in this way.
I understand well your difficulty and I am aware of your sufferings on this account. However, if God wishes it and it relieves me, you will have pity on me, will you not? When I am released you will see that I will do far more for you than you have ever done for me. I already pray much for you.
Where is Sister --?
In the lowest Purgatory, where she receives no benefit from anyone's prayers. God is often displeased, if one may speak thus, when many religious come to die, because He has called these souls to Himself that they might serve Him faithfully on earth and go straight to Heaven at the moment of death, but because of their infidelity, they have to stay long in Purgatory - far longer than people in the world who have not had so many graces.
1879, Retreat in September. We see St. Michael as we see the angels. He has no body. He comes to get the souls that have finished their purification. It is he who conducts them to Heaven. He is among the Seraphim as Monsignor said. He is the highest angel in Heaven. Our own Guardian Angels come to see us but St. Michael is far more beautiful than they are. As to the Blessed Virgin, we see her in the body. She comes to Purgatory on her feasts and she goes back to Heaven with many souls. While she is with us we do not suffer. St. Michael accompanies her. When he comes alone, we suffer as usual. When I spoke to you of the great and the second Purgatory, it was to try to make you understand that there are different stages in Purgatory. Thus I call that stage of Purgatory “great” or “worst” where the most guilty souls are, and where I stayed for two years without being able to give a sign of the torments I was suffering. The year when you heard me groaning, when I began to speak to you, I was still in the same place.
In the second Purgatory, which is still Purgatory but very different from the first, one suffers a great deal, but less than in the great place of expiation. Then there is a third stage, which is the Purgatory of desire, where there is no fire. The souls who did not desire Heaven ardently enough, who did not love God sufficiently, are there. It is there that I am at this moment. Further, in these three parts of Purgatory, there are many degrees of variation. Little by little, as the soul becomes purified, her sufferings are changed.
You sometimes say to me that the perfecting of a soul is a long process and you are also astonished that after so many prayers, I am so long deprived of the sight of God. Alas, the perfecting of a soul does not take any less time in Purgatory than upon earth. There are a number of souls, but they are very few, who have only a few venial sins to expiate. These do not stay long in Purgatory. A few well-said prayers, a few sacrifices soon deliver them. But when there are souls like mine - and that is nearly all whose lives have been so empty and who paid little or no attention to their salvation - then their whole life has to be begun over again in this place of expiation. The soul has to perfect itself and love and desire Him, whom it did not love sufficiently on earth. This is the reason why the deliverance of some souls is delayed. God has given me a very great grace in allowing me to ask for prayers. I did not deserve it, but without this I would have remained like most of those here, for years and years more.”
http://www.mysticsofthechurch.com/2012/04/amazing-stories-from-purgatory-and.html