December 22, 2017
There are two separate obligations that must be fulfilled for the Fourth Sunday of Advent (Sunday, Dec. 24) and Christmas (Monday, Dec. 25). Given that Christmas falls the day after the Fourth Sunday of Advent this year, the expectation might be confusing to some.
The Sunday obligation can be fulfilled by going to Mass on Saturday evening (Dec. 23) or anytime on Sunday (Dec. 24). The Christmas obligation can be fulfilled by going to Mass on Sunday evening or anytime on Monday (Dec. 25). So, to give two examples, the faithful may attend a Christmas Eve Vigil Mass to fulfill the Sunday obligation and then go to a Christmas Day Mass on Monday to fulfill the Christmas obligation; or attend Mass on Sunday morning, Christmas Eve, to fulfill the Fourth Sunday of Advent obligation and then attend the Christmas Eve Vigil Mass that evening to fulfill the Christmas obligation. (If this combination is chosen, the Eucharist may be received at both Masses, providing those are the only two instances of receiving the Lord in the Eucharist that day.)