Catechism of the Catholic Church §502 — excerpt
The eyes of faith can discover in the context of the whole of Revelation the mysterious reasons why God in his saving plan wanted his Son to be born of a virgin.
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.