The Solemnity of the Immaculate Conception, also called Immaculate Conception Day, celebrates the sinless lifespan and Immaculate Conception of the Blessed Virgin Mary. Solemnity of the Immaculate Conception of the Blessed Virgin Mary. This Holy Day of Obligation will be celebrated on Friday, December 8, at 7 a.m. at St. Lawrence, 10 a.m. at St. Boniface (SJNRA Mass), and at 5:30 p.m. at St. Boniface.