Catechism of the Catholic Church §460 — excerpt
The Word became flesh to make us "partakers of the divine nature": "For this is why the Word became man, and the Son of God became the Son of man: so that man, by entering into communion with the Word and thus receiving divine sonship, might become a son of God."
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.
Also cites: St. Irenaeus, Adv. haeres. 3, 19, 1: PG 7/1, 939 · St. Athanasius, De inc. 54, 3: PG 25, 192B · St. Thomas Aquinas, Opusc. 57, 1-4