Use and authority of the creed
As already indicated, we must turn to the ritual of Baptism for the most primitive and important use of the Apostles' Creed. It is highly probable that the Creed was originally nothing else than a profession of faith in the Father, Son, and Holy Ghost of the baptismal formula. The fully developed ceremonial which we find in the seventh Roman Ordo, and the Gelasian Sacramentary, and which probably represented the practice of the fifth century, assigns a special day of "scrutiny", for the imparting of the Creed (traditio symboli), and another, immediately before the actual administration of the Sacrament, for the redditio symboli, when the neophyte gave proof of his proficiency by reciting the Creed aloud. An imposing address accompanied the traditio and in an important article, Dom de Puniet (Revue d'Histoire Ecclesiastique, October, 1904) has recently shown that this address is almost certainly the composition of St. Leo the Great. Further, three questions (interrogationes) were put to the candidate in the very act of baptism, which questions are themselves only a summary of the oldest form of the Creed. Both the recitation of the Creed and the questions are still retained in the Ordo baptizandi of our actual Roman ritual; while the Creed in an interrogative form appears also in the Baptismal Service of the Anglican "Book of Common Prayer".
Outside of the administration of baptism the Apostles' Creed is recited daily in the Church, not only at the beginning of Matins and Prime and the end of Compline, but also ferially in the course of Prime and Compline. Many medieval synods enjoin that it must be learnt by all the faithful, and there is a great deal of evidence to show that, even in such countries as England and France, it was formerly learnt in Latin. As a result of this intimate association with the liturgy and teaching of the Church, the Apostles' Creed has always been held to have the authority of an ex cathedra utterance. It is commonly taught that all points of doctrine contained in it are part of the Catholic Faith, and cannot be called in question under pain of heresy (St. Thomas, Summa Theologica, II-II:1:9). Hence Catholics have generally been content to accept the Creed in the form, and in the sense, in which it has been authoritatively expounded by the living voice of the Church. For the Protestants who accept it only in so far as it represents the evangelical teaching of the Apostolic Age, it became a matter of supreme importance to investigate its original form and meaning. This explains the preponderating amount of research devoted to this subject by Protestant scholars as compared with the contributions of their Catholic rivals.
from http://www.newadvent.org/cathen/01629a.htm
