Chapter 2 — Part I: The Creed — Introduction on Faith and the Creed
Section 6. This profession of Christian faith and hope, drawn up by themselves, the Apostles called a symbol; either because it was made up of various parts, each of which was contributed by an Apostle, or because by it, as by a common sign and watchword, they might easily distinguish deserters from the faith and false brethren unawares brought in, adulterating the word of God, from those who had truly bound themselves by oath to serve under the banner of Christ.