Catechism of the Catholic Church §1235 — excerpt
The sign of the cross, on the threshold of the celebration, marks with the imprint of Christ the one who is going to belong to him and signifies the grace of the redemption Christ won for us by his cross.
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.