Purgatory doesn’t take away from Christ’s work, but rather it is Christ’s work. It is not something the Church created in order to force people to work their way into heaven. Purgatory is instead something God created so that the grace his Son obtained for us on the cross could make us “holy and blameless and irreproachable before him” (Col. 1:22), free from the pain and penalty of sin, and ready to enter into eternal glory with Christ our Lord.
