On December 8 every year, Catholics celebrate the Solemnity of the Immaculate Conception by attending Mass. A catechumen might ask, "Why is this feast day so important?" The Catechism of the Catholic Church 491 explains:
Eternal rest grant unto them, O Lord. And let the perpetual light shine upon them.
And may the souls of all the faithful departed, through the mercy of God, rest in peace. Amen.