Catechism of the Catholic Church §225 — excerpt
It means knowing the unity and true dignity of all men: everyone is made in the image and likeness 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.