Saturday, December 8th is the Feast Of The Immaculate Conception of the Blessed Virgin Mary, a Holy Day Of Obligation. This feast references Mary’s conception in her mother’s womb without the stain of original sin.
Friday, December 7th Mass at St. Mary's is:
Saturday, December 8th Mass at St. Peter is:
Saturday, December 8th Mass at St. Mary is:
12:00 PM Noon
Since a "grave cause" is needed to excuse one from this obligation, it would be a serious or mortal sin to willfully skip Mass on Sunday or a Holy Day of Obligation, as the Church teaches. Reasons such as the necessity to work to support one's family, child care, personal sickness or the care of the sick, necessary travel etc. would excuse a person on a particular occasion.
Please note that the Saturday 4:00 P.M. Mass at St. Mary's and 5:00 P.M. Mass at St. Peter's will occur at the ordinary scheduled time and do not meet the obligation of attending the Feast Of The Immaculate Conception Holy Day Mass.