Q. Why do countries have different Holy Days of Obligation?
A. Holy Days of Obligation are feast days in the Church’s calendar fixed by a certain date on which Holy Mother Church expects her children to attend the liturgical celebrations of that day. All Catholics are obligated, under pain of the normal conditions of mortal sin, to attend the Holy Mass every Sunday. However, there are important feasts on the calendar that would more frequently fall on days of the week and not on Sunday.
Following the Second Vatican Council, the Holy See eventually empowered the National Conferences of Bishops to assign for the people of their respective countries individual expectations of which solemnities would be obligatory. There were originally ten holy days in the calendar. In some jurisdictions, they have all been kept. In others, some have been dropped completely or have been transferred to the nearest Sunday.
In Canada, for instance, our bishops discerned that it was most important for Catholics to attend the Holy Mass on the Nativity of our Lord (Christmas) and the Solemnity of Mary, Mother of God (1 January). Many of the other original feasts are now observed on the nearest Sunday, like the Ascension of our Lord and Corpus Christi. Some days like the Assumption of the Blessed Virgin Mary (15 August) and All Saints (1 November) have just been dropped from the list of obligatory.
That being said, the Holy Mass is an obligation we should appreciate and enjoy. Therefore, our attendance at it on days of great solemnity should be for us an honour!