Catechism of the Catholic Church §1262 — excerpt
The different effects of Baptism are signified by the perceptible elements of the sacramental rite. Immersion in water symbolizes not only death and purification, but also regeneration and renewal.
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.