Catechism of the Catholic Church §579 — excerpt
This principle of integral observance of the Law not only in letter but in spirit was dear to the Pharisees. By giving Israel this principle they had led many Jews of Jesus' time to an extreme religious zeal.
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.