In the traditional, Extraordinary Form, calendar, this Sunday’s Mass uses texts for the Fifth Sunday “left over” after Epiphany. Yes, you read that right. Sometimes it is called the “Fifth Resumed” or even “Where-do-I-find-that-in-my-Missal?” Sunday.
How can Sundays be “left over”? Perpend!
The structure of the liturgical calendar depends on the vagaries of the moon. Each year, Easter falls according to when the spring full moon occurs. Since the moon isn’t always full on the same date, Easter Sunday shifts. Lent, however, has a fixed length. Thus, the beginning of Lent slides around, earlier or later, depending on that spring full moon.
At the other end of the equation, Epiphany is a fixed date: January 6. Since the beginning of Lent slides around, the time between Epiphany and Ash Wednesday (and Septuagesima three weeks before), is longer or shorter depending on when the spring full moon rises. As many as six Sundays (the second through to the sixth Sunday after Epiphany) can fall between Epiphany and Septuagesima Sunday. Septuagesima can crop up any time from January 18 to February 22. Therefore, when Lent begins early the formularies for as many as four Sundays after Epiphany, slated to be celebrated up to Septuagesima, must be skipped.
On the other end of the Lent/Easter cycle, Pentecost also shifts its date because Pentecost is always the same number of days after the movable Easter. The 24 Sundays allotted after Pentecost are not enough to get us all the way to the end of the liturgical year, back around to Advent. Depending on the date of the spring full moon, there can be a gap of several Sundays between the 22nd after Pentecost and the Last Sunday before Advent. Therefore, Holy Church uses those movable Sundays left over after Epiphany as fillers until the final Sunday of the year, which liturgically is always the 24th Sunday after Pentecost, even if it isn’t ordinally the 24th.
Ergo, at the end of the Church’s year, in the traditional calendar, we get “left over” Sundays. See? It’s easy!
Speaking of spring, if I remember correctly, Joseph Ratzinger wrote in his book The Spirit of the Liturgy about the fittingness of having Sundays after Epiphany observed in both spring or autumn, for Northern spring and autumn are, in the Southern hemisphere, autumn and spring. In springtime we plant last year’s autumn seeds; in autumn we harvest seeds from spring’s sowing.
