Holy days of obligation are days set aside by the Church when the faithful attend Mass. In addition to Sundays, the days observed as holy days of obligation in the United States are:
Each Sunday, the faithful gather for worship in honor of Christ’s Resurrection. The additional holy days of obligation listed above are days dedicated to important events connected to the life of Jesus or persons linked to him. As it states in the Code of Canon Law, the faithful are obliged to participate in Mass. Insofar as possible, they are also to abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord’s Day, or the suitable relaxation of mind and body (canon 1247).
By decision of the United States Conference of Bishops and confirmation by the Holy See, whenever the Solemnities of Mary, Mother of God (January 1), the Assumption of the Blessed Virgin Mary (August 15), or All Saints (November 1) fall on a Saturday or a Monday, the obligation to attend Mass is lifted.