Though holy days are a characteristic of the universal Church, local custom can bring about changes to the list.
These days are called holy days of obligation and the Church equates the importance of these days to a Sunday.
A precept of the Church explains, “On Sundays and other holy days of obligation the faithful are bound to participate in the Mass.”
One of the chief reasons behind these holy days is to highlight a specific aspect of the life of Christ or to give honor to the role of the Blessed Virgin Mary and the communion of saints.
These days are for the spiritual benefit of Christ’s flock and are opportunities to receive grace.
Holy days of obligation are currently governed by the local bishops’ conferences and can vary from country to country. For example, December 12 (feast of Our Lady of Guadalupe) is a holy day of obligation in Mexico (Our Lady of Guadalupe is also the patron of the country). Meanwhile, Dec. 8, the feast of the Immaculate Conception, is a day of obligation in the United States (and Our Lady of the Immaculate Conception is the patron of the US).
In 1991 the USCCB issued new norms regarding holy days of obligation and listed the following:
January 1, the Solemnity of Mary, Mother of God
Thursday of the Sixth Week of Easter, the Solemnity of the Ascension
August 15, the Solemnity of the Assumption of the Blessed Virgin Mary
November 1, the Solemnity of All Saints
December 8, the Solemnity of the Immaculate Conception
December 25, the Solemnity of the Nativity of Our Lord Jesus Christ
Whenever January 1, the Solemnity of Mary, Mother of God, or August 15, the Solemnity of the Assumption, or November 1, the Solemnity of All Saints, falls on a Saturday or on a Monday, the precept to attend Mass is abrogated.
Since the proclamation of these norms, the Solemnity of the Ascension has been transferred to a Sunday in most dioceses in the United States.
These days can be changed or added to according to local custom. For example, in Malta the Church celebrates the Shipwreck of St. Paul in Malta on February 1o as a holy day of obligation and Ireland celebrates (not surprisingly) the feast of St. Patrick as a holy day.