Catechism of the Catholic Church §590 — excerpt
Only the divine identity of Jesus' person can justify so absolute a claim as "He who is not with me is against me"; and his saying that there was in him "something greater than Jonah,.
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: Cf.Mt 12:6, 0, 36, 37, 41-42
