There is one Church but it exists, for now, under three states.

The Church of Heaven is the Church under the state of enjoyment of God’s vision. The Church “Militant” is the Church under the state of pilgrimage, and often persecution, here below on this earth. The Church of Purgatory is the Church under the state of suffering for sins committed by individual members.

All Souls’ Day is the beginning, in its way, of the month of penance offered for all souls that are or will be in the  Church of Purgatory.

That’s not everyone. Those who die in an act of pure love go straight to the Church of Heaven. That is, one can assume that anyone in a habitual union with God (those on the “unitive” way in classical Latin Church terminology, following Dionysius – in a real union of wills with Jesus) whose last act follows through on that union goes straight to Heaven. That’s actually the normal way. I don’t say it’s the most common way. But it’s normal. It should be normative, because the “normal” way of being a Christian is to pass through the dark nights and enter into the contemplative or “unitive” way of love and abandonment, to “be perfect” as our Father is perfect (or to at least walk on the path detached from creatures and our own will, which allows us to slowly become perfect).

Not all souls go to Purgatory. It’s not even “normal” or “normative” to have to go to Purgatory; Christianity has more hope than that. But there are indeed souls who, for whatever reason, die as beginners in the spiritual life (having not started or barely started a dark night) or die on the “illuminative way” (having passed through, or starting to pass through, the first dark night only). They will go to Purgatory, because, to enjoy God with all our heart and mind, we have to be cleaned up – either in this life or in the next. We will be purged of our sins. Better now that later, but if it’s later, then at least it will happen. That’s the beauty of Purgatory. If we don’t enter onto the “contemplative” or “unitive” way and then die while acting that out, then we still can enjoy God. It takes Purgatory. But God still gives us everything.

Praying for all souls means experiencing the union of the Church of Heaven, the Church of Purgatory, and the Church in pilgrimage on earth. And it is by most closely and fully entering into contemplation that we are of most use to those souls who, while holy, are not yet detached from all that is not God and have gone to Purgatory.