I was mainly interested in why this list was chosen. Perhaps my assumption of these days being more important than others (thus obligatory) is wrong? It’s interesting to learn also that the list of days varies by country. It just seems like some crucial days are missing – and I’m not sure why Corpus Christi would be more important than Pentecost (say), or why the beginning of Lent (Ash Wednesday) is less important than All Saints. I appreciate everyone helping me understand!
I would like to try and type a longer response when I have more time, but the short of it is:
Pentecost falls on a Sunday and all Sundays are days of obligation
At one time, very many of these days that you note were HDoO. The HDoO as you know, is twofold (1 attend Mass (2) abstain from servile work. The Church gradually decreased this number so as not to impose a burden upon the working faithful (of course, one can argue that the excessive pruning seen in some countries today is not desirable either)
Anyhow, as to the list:
Almost all the feasts with the rank of “solemnity” are Holy Days of Obligation. The ones that aren’t are either Sundays (on which they are then, by default) or these: the Sacred Heart, the Nativity of St. John the Baptist, and the Annunciation.
The Holy Days of Obligation are for the principal mysteries of the life of Christ, hence most of those which are not recalled on Sundays are HDoO.
For the Virgin Mary, her feast par excellence, from which derives all her privileges- the Mother of God - and the two principal mysteries of her life- her Conception and Assumption.
Ss. Peter and Paul because they are the patron saints of the Roman Church and, despite the fact that it is now spread over the whole globe, it is still Roman
St. Joseph because the last few Popes (relatively speaking) have emphasized his role as guardian of the Church and the family. I suppose it was either him or St. John the Baptist, and there is a greater devotion and symbol connected to him. Technically though, the Church has usually placed St. John the Baptist ahead of St. Joseph ** on account of him being the messenger, Christ’s words about him and the fact that he was born with sin.
And All Saints because that is a “one size fits all” day to venerate and recognize that we are part of the glorious communion.
I would argue that the Sacred Heart is not observed because it is an “idea” feast. So is Corpus Christi for that matter, but that recalls the mystery of the Eucharist which is the principal treasure of the Church, and also has a much longer and venerable history of being marked by solemnity. The Annunciation was actually removed by St. Pius X - I’m guessing that a possible reason mught be that if one wishes to curtail the number of days of obligation, the the Annunciation and the Nativity are on par with each other.
The Triduum (Holy Thursday to Saturday) was removed back in the 17th century. I suppose one reason for that was that the liturgy for these then were FAR longer than they are today. (Though IMHO, if you’re going to attend a long liturgy, I cant think of any days more appropriate). Another explanation that I’ve heard, is that the Church only solemnizes festal days with the obligation (attend Mass and abstain from servile work) not penitential days. HDoO are, to put it in a certain way, “second Sundays” and so are expressions of joy.
** the Church puts certain saints in a heirachy of precedence. First (of course!) comes the BVM. Then come the angels, St. John the Baptist, then St. Joseph, then the Apostles, then martyrs and so on. You can look at the
Litany of Saints for an indication of this order.