Holy Day of Obligation Mass at St. Catherine: 8:30 a.m. December the 9th, the Church celebrates the Solemnity of the Immaculate Conception of the Blessed Virgin Mary, and it is a holy day of obligation. On this feast, we celebrate Mary’s conception free from the stain of Original Sin, and we recognize that Mary’s life began the moment she was conceived in the womb of St. Anne. So, too, does every human life begin at the moment of fertilization: “You formed my inmost being; you knit me in my mother’s womb” (Ps 139:13).