A reader writes:
Lent is a time of following the Lord’s 40 days and 40 nights in the desert; a time of self-denial and penance, leading to new life at Easter. The point of this time period is to spend 40 days in spiritual discipline. If you count from Ash Wednesday to Holy Saturday (inclusive), but excluding Sundays, you arrive at 40. Again, the point is to spend 40 days of penance before Easter. That the number 40 neatly fits within the technical bounds of Lent is not, it seems to me, the point. Counting in this fashion is yet another support to the notion that Sundays, though certainly within the season of Lent, are not observed as days of penance, but rather days of celebrating the Lord’s Day.
It is true, poetically speaking, that "Lent is a time of following the Lord’s 40 days and 40 nights in the desert; a time of self-denial and penance, leading to new life at Easter." However, the Church’s law does not appear to support the claim that "The point of this time period is to spend 40 days in spiritual discipline . . . before Easter." As noted above, there are more than forty penitential days in this period, and penitential days are days of spiritual discipline. I don’t think that the Church would regard any particular number of days as "the point," but it has established more than forty in this period.
It is true that "If you count from Ash Wednesday to Holy Saturday (inclusive), but excluding Sundays, you arrive at 40," but this does not correspond to the Church’s law. One can say that "Counting in this fashion is yet another support to the notion that Sundays, though certainly within the season of Lent, are not observed as days of penance, but rather days of celebrating the Lord’s Day," but this posits a false opposition between Sunday being a day of celebration and Sunday being a day of penance. It can be, and during Lent is, both.
The Church’s law is clear that Sundays in Lent both involve the celebration of the Resurrection and the practice of penitence. The penitential practice of the Church is even reflected in the liturgy on Sundays of Lent, as illustrated by the fact that the Gloria and the Alleluia are omitted, purple vestments are worn, and special readings (e.g., this coming Sunday is the "unless you repent you also will perish" passage). It’s also worth noting that, as the General Instruction provides, "Rose may be used, where it is the practice, on Gaudete Sunday (Third Sunday of Advent) and on Laetare Sunday (Fourth Sunday of Lent)" (GIRM 346f). The standard interpretation of the use of rose vestments on Laetare Sunday is that it is a lessening of the penance that is already in place.
The decisive fact, though, is simply that the law (quoted above) provides that "The penitential days and times in the universal Church are every Friday of the whole year and the season of Lent." It doesn’t say "except Sundays."
Hope this helps!