Monday, December 9, 2024 is a holy day of obligation in honor of the Immaculate Conception of the Blessed Virgin Mary.
This year the nation’s patronal feast falls on a Sunday, December 8. When a solemnity falls on a Sunday, it usually takes precedence over the Sunday it falls on. However, the Sundays of Advent, Christmas, Lent and Easter cannot be supplanted by a Solemnity. This is the case with the commemoration of the Immaculate Conception of the Blessed Virgin Mary.
In the past it was assumed that when this feast was transferred the “obligation” to attend Mass was removed. This was based on the similar practice we follow when, for example the solemnity All Saints (a “holy day of obligation”) falls on a Saturday or Monday. When that happens, the feast is celebrated but the “obligation” to attend is removed. However, the USCCB has been informed by the Holy See that this cannot be applied to the commemoration of the Immaculate Conception. Thus, for this feast the obligation remains even if the actual day is moved to Monday, December 9.
Consequently, the Solemnity of the Immaculate Conception is always a “holy day of obligation” even when it is moved because it cannot be celebrated on a Sunday during Advent.