Once we’ve waded through the directives on solemnities, feasts, Sundays, and obligatory memorials, what happens when there’s a true choice for Mass texts? You can just let the ordo tell you what to do. Or you can learn the principles and solve it yourself. Let’s read:
355. On Optional Memorials,
a) On the weekdays of Advent from December 17 to December 24, on days within the Octave of the Nativity of the Lord, and on the weekdays of Lent, except Ash Wednesday and during Holy Week, the Mass texts for the current liturgical day are used; but the Collect may be taken from a Memorial which happens to be inscribed in the General Calendar for that day, except on Ash Wednesday and during Holy Week. On weekdays of Easter Time, Memorials of Saints may rightly be celebrated in full.
b) On weekdays of Advent before December 17, on weekdays of Christmas Time from January 2, and on weekdays of Easter Time, one of the following may be chosen: either the Mass of the weekday, or the Mass of the Saint or of one of the Saints whose Memorial is observed, or the Mass of any Saint inscribed in the Martyrology for that day.
c) On weekdays in Ordinary Time, there may be chosen either the Mass of the weekday, or the Mass of an Optional Memorial which happens to occur on that day, or the Mass of any Saint inscribed in the Martyrology for that day, or a Mass for Various Needs, or a Votive Mass.
In addition to the above considerations for the important observances of the liturgical year, there is a value in maintaining the integrity of the daily Lectionary cycle. The principle harkens to Vatican II:
If he celebrates with the people, the Priest will take care not to omit too frequently and without sufficient reason the readings assigned each day in the Lectionary to the weekdays, for the Church desires that a richer portion at the table of God’s Word should be spread before the people.[Sacrosanctum Concilium 51]
Where I’ve served, I’ve not known a Mass for the Dead to be chosen, except for a funeral.
For the same reason he should choose Masses for the Dead in moderation, for every Mass is offered for both the living and the dead, and there is a commemoration of the dead in the Eucharistic Prayer.
Where, however, the Optional Memorials of the Blessed Virgin Mary or of the Saints are dear to the faithful, the legitimate devotion of the latter should be satisfied.
“Legitimate” may not be the best choice of words here. “Sincere” is widespread, but do such devotions develop to the point where there is true interest in delving deeper into the spirituality of the saint? Does it go beyond culture?
Moreover, as regards the option of choosing between a Memorial inscribed in the General Calendar and one inserted in a diocesan or religious Calendar, preference should be given, all else being equal and in keeping with tradition, to the Memorial in the particular Calendar.