Chapter 15 — Part II: The Sacraments — Introduction on the Sacraments in General
Section 29. A fourth reason why the institution of the Sacraments seems necessary is that there may be certain marks and symbols to distinguish the faithful; particularly since, as St. Augustine observes, no society of men, professing a true or a false religion, can be, so to speak, consolidated into one body, unless united and held together by some bond of sensible signs. Both these objects the Sacraments of the New Law accomplish, distinguishing the Christian from the infidel, and uniting the faithful by a sort of sacred bond.