Dec. 8 is usually celebrated as the Solemnity of the Immaculate Conception of the Blessed Virgin Mary. Because Dec. 8 falls on Sunday this year, the Church has moved that feast to Monday, Dec. 9, so as not to conflict with the Second Sunday of Advent. It remains a Holy Day of Obligation, so we are to attend Mass that day. Some parishes may have a Holy Day Mass on Sunday evening, and that is acceptable also.
    
The Church teaches that because Mary was to be the mother of the Son of God, it was fitting that she should be preserved from all sin, Original and personal, so that she could be a pure vessel for Jesus to come into the world. Therefore, God preserved Mary from Original Sin from the moment of her conception in the womb of her mother, St. Anne. This is the meaning of her Immaculate Conception.
   
The Immaculate Conception is the first direct act by God in bringing salvation into the world. As such, it is celebrated as one of the most important works in salvation history. Mary herself, at her appearance to St. Bernadette, when asked who she was, replied, “I am the Immaculate Conception.” Although the doctrine of the Immaculate Conception was known, it had never been used as a title for Mary. Now she herself claimed that not only was she immaculately conceived, she was, in fact, the Immaculate Conception.