Saturday, December 8th is the Solemnity of the Immaculate Conception of the Blessed Virgin Mary and is a Holy Day of Obligation.
Failure to attend Mass on a Holy Day of Obligation without a serious reason is a mortal sin.
A Vigil Mass will be offered on Friday, December 7th at 6:30 PM
Masses will also be offered on Saturday, December 8th at 7:30 AM and 10:00 AM.
The 5:30 PM Vigil Mass on Saturday, December 8th, fulfills the Sunday Obligation as normal, but does not fulfill the obligation for the Immaculate Conception Holy Day.