Some time ago, I got the message that I was to pray for souls. Very simple, just "You are to pray for souls." Ever since, my devotion to praying for the souls in Purgatory has increased, and I pray for the souls of my family and friends as well as praying for persecuted Christians.
I have a wonderful book which I recommend, it is a collection of 365 daily reflections, written by Susan Tassone, entitled Day By Day for the Holy Souls in Purgatory.
I love the reflection for today, because it explains the simplicity of Purgatory so well:
The souls are in a fiery prison, and our good God, to open that prison, asks only a prayer from us. Can we refuse this prayer? (Blessed Mary of Providence).
The prison of Purgatory is one of our own making. The fire is the longing to be in the presence of the Lord. The key to release is prayer. Pray for those suffering souls whose own prayers can no longer help bring them to the Lord they so intensely love.