Catechism of the Catholic Church §1177 — excerpt
The hymns and litanies of the Liturgy of the Hours integrate the prayer of the psalms into the age of the Church, expressing the symbolism of the time of day, the liturgical season, or the feast being celebrated.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.