From Paschale Solemnitatis:
23. The first Sunday of Lent marks the beginning of the annual Lenten observance. In the Mass of this Sunday there should be some distinctive elements which underline this important moment, e.g., the entrance procession with litanies of the saints. During the Mass of the first Sunday in Lent, the bishop should celebrate the rite of election in the cathedral or in some other church, as seems appropriate.
Apart from fasting, abstinence and penance, which reside in the “Lex Vivendi” of the liturgy, within the liturgical experience, there exists an invitation by the Congregation for Divine Worship to mark the First Sunday of Lent with distinctive elements so as to heighten the experience that we are in the period of Lent.
We have practiced singing the Litany of the Saints to accompany the Entrance Procession in previous years, however this year, we will be adopting the Lenten Prose (notation 1, notation 2) instead, at the request of the parish leaders.