The Following is an excerpt from Great Lent, by Alexander Schmemann
From Chapter 2: Preparation for Lent
The next Sunday [after Zaccheus Sunday] is called the "Sunday of the Publican and the Pharisee." On the eve of this day, on Saturday at Vespers, the liturgical book of the Lenten season-- the Triodion-- makes its first appearance and texts from it are added to the usual hymns and prayers of the weekly resurrection service. The develop the next major aspect of repentance: humility.