Catechism of the Catholic Church

Communion with the dead. "In full consciousness of this communion of the whole Mystical Body of Jesus Christ, the Church in its pilgrim members, from the very earliest days of the Christian religion, has honored with great respect the memory of the dead; and because it is a holy and a wholesome thought to pray for the dead that they may be loosed from their sins' she offers her suffrages for them." Our prayer for them is capable not only of helping them, but also of making their intercession for us effective. (1371, 1032, 1689)