Popular piety also calls them the "poor souls," and there's something touching in that. They're poor because they can no longer do anything for themselves. During life we could pray, repent, receive the sacraments, give alms and make up for what we'd done. They've run out of that kind of time. They have everything to hope for and nothing in their hands to offer, and that's why the Church has always said they need us.
Why "holy"?
It's called the month of the Holy Souls, and it may seem a strange word for people who aren't yet perfectly purified. The reason is simple. They are in God's friendship, they are certain of salvation, and they are being made holy. Nobody in Purgatory is in danger of being lost. In one sense they're safer than we are, because their destiny is settled.
The great mystic Catherine of Genoa wrote that the souls in Purgatory can't think of themselves as being there for any fault of their own, nor turn their attention to anything else. They are fixed in love, and in a kind of joy. This is why the tradition speaks of them with reverence, not pity alone.
Who is in that number?
Nobody knows by name. The Church canonizes saints but has never declared any person to be in Purgatory, as we've seen. What we know is who the souls are in general: the faithful who died in God's grace and friendship, but whose love isn't yet whole. Some died yesterday. Some died centuries ago, forgotten by everyone on earth. Some had many prayers said for them, and some had none.
That last group is why the Church speaks so often of the "forgotten souls," those with no one left to remember them: the person whose family has died out, the stranger buried without a funeral, the soldier whose name wasn't recorded. They're as much in need of prayer as anyone, and often more.
Do they know us?
The Church doesn't define how the souls experience our prayers or what they know of us. What she teaches is that we're united with them in the communion of saints (CCC 954-959). Many saints and theologians have held that the Holy Souls can pray for us as well, and the Catechism says our prayer for the dead can make their intercession on our behalf effective (CCC 958). The Church doesn't require us to ask for their help, and she hasn't defined the matter, but a long tradition of Catholics does it, and there's nothing in it contrary to the faith. It's a sweet and reasonable thing to do, to pray for someone and ask them to pray for us in return.
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