Throughout Church history, the liturgical calendar has been filled with feasts, memorials, and solemnities commemorating saints and Scriptural events. Some days have greater importance then others, and they are instated as Holy Days of Obligation, in which the faithful attend Mass and celebrate like on Sundays.

However, the local conference of bishops has the ability to remove a day from the “obligation” list or transfer the feast to Sunday, as long as they have the prior approval of the Vatican. This is done for a variety of reasons, but in the United States, it is primarily a pastoral consideration. Decreased priest numbers leading to decreased Mass time availability, as well as work and school day complications, led to declining numbers at midweek Masses. To enable as many of the faithful as possible to participate in the liturgy, some feasts are moved from a weekday to Sunday, like the Ascension of the Lord.