This year, Christmas is the day after the Fourth Sunday of Advent. So how are we called to meet our holy days of obligation? One is expected to attend a Mass that fulfills the obligation for the Fourth Sunday of Advent and one that fulfills the obligation for Christmas. A Mass can only fulfill one obligation. Therefore, to fulfill our holy days of obligation, we are to attend two Masses.
Option 1: Attend the Vigil Mass on Sat., Dec. 23 for the Fourth Sunday of Advent. Then attend Christmas Eve Vigil Mass on Sunday, Dec. 24 OR Christmas Day Mass, on Mon., Dec. 25.
Option 2: Attend Mass for the Fourth Sunday of Advent on Sunday morning, December 24. Then attend Christmas Eve Vigil Mass on Sunday, Dec. 24 OR Christmas Day Mass on Mon., Dec. 25.