A question that often arises when Christmas Day falls on a Monday is, “If I go to Mass, on Sunday, December 24 in the morning, do I still need to attend Mass in the evening or on Christmas Day?” The answer is “Yes.” The Masses celebrated on Saturday, December 23 at 4:00 p.m. and on Sunday morning December 24, at 9:00 and 11:00 are for the Fourth Sunday of Advent and fulfill the Sunday obligation. To fulfill the obligation of attendance at Christmas Mass one must attend either one of the Masses on December 24 at 4:00 p.m., 6:00 p.m., 10:30 p.m. or on December 25 at 9:00 a.m. or 11:00 a.m. In other words, you must attend one Mass celebrating the Fourth Sunday of Advent and one Mass celebrating Christmas.
Fr. David