In the traditional Catholic calendar, today was Septuagesima, or “Seventieth.” This is a misnomer, because it is certainly NOT the 70th day before Easter. The 1912 Catholic Encyclopedia, as reprinted at New Advent suggests that it may just be named this as part of a series (since Lent is Quadragesima, or Forty), or that it’s possible that this is the earliest that Lent began for some early Christians (who would have excepted Thursday, Saturday, and Sunday from counting for the fast). It comes down to this being one of those tradition-inertia things that we have held onto.
In any case, what it does mean is that we’re in pre-Lent. It is a reminder that we should begin preparing ourselves for the great fast that is coming. We have three Sundays to plan out our Lenten observances, and really figure out how to get ourselves ready for Easter through prayer, fasting, and almsgiving. As a sign of this, the liturgy (at least in the Extraordinary Form of the Catholic Mass) changes. We lose the Gloria at mass. We also lose the Alleluia, which is replaced by a tract (essentially, an extended psalm without antiphon responses) in mass. Traditionally, the Alleluia is “buried” the Saturday before Septuagesima (no, really, a paper or banner with the word is buried, to be brought out again at Easter). The priest wears purple. In many ways, it starts to look like Lent, even if we aren’t quite into the full-blown Lenten season yet.
Still, Lent is coming, and the liturgical changes serve as that wake up call to get us thinking about it.