As Catholics, we say we believe in the “communion of saints.” We make that affirmation whenever we say the Apostles’ Creed. The Catechism tells us that the communion of saints is “the Church” — which means the whole Church, which is composed of those who are already in heaven with the Lord (“the Church triumphant”), those who are being made ready for heaven by passing through the purifying fires of purgatory (“the Church suffering”), and those of us who are still here on earth (“the Church militant”).
And we’re all connected! That’s the good news. Spiritually speaking, nothing — not even physical death — completely severs the bond between those who are in Christ.
This is why we ask the saints in heaven to pray for us. We believe that their prayers before the throne of God can bring us graces here in this world. And they can! They can because we’re still connected to them in the spiritual realm.
We also believe that our prayers and sacrifices can directly benefit the souls in purgatory — helping them to be purified and thus get to heaven more quickly. This is why we pray and have Masses said for the dead: it’s to help our deceased brothers and sisters who are currently undergoing this final sanctification. Remember, those who are in heaven don’t need our prayers because they’re already in the kingdom, and those in hell can’t be helped by our prayers because hell is eternal.
The only ones that we in the Church militant can help are those in the Church suffering — and vice versa. The souls in purgatory, according to many of the canonized saints, can also pray for us; they just cannot pray for themselves. They need us to do that for them — and not only on All Souls Day and during the month of November, but throughout the year.