Chapter 11 — Part I: The Creed — Article IX: The Holy Catholic Church; the Communion of Saints
Section 39. It should not be deemed a matter of surprise that the Church, although numbering among her children many sinners, is called holy. For as those who profess any art, even though they depart from its rules, are still called artists, so in like manner the faithful, although offending in many things and violating the engagements to which they had pledged themselves, are still called holy, because they have been made the people of God and have consecrated themselves to Christ by faith and Baptism. Hence, St. Paul calls the Corinthians sanctified and holy, although it is certain that among them there were some whom he severely rebuked as carnal, and also charged with grosser crimes.