(Taken from Notes Made at the Conferences of Dom Prosper Guéranger)
The Gospel is followed by the Credo. The object proposed by the recitation of the Credo is to lead the Faithful to confess the Faith; and since their Faith is based upon the holy Gospel, the Credo comes immediately after the sacred text has been read. It is but right, that the Faithful should utter this profession of faith against the heresies that have been broached.
[See note below regarding this paragraph] The Credo is to be said, not only on all Sundays, but, moreover, on the feasts of the Apostles, who preached the faith; on the feasts of Doctors, who defended it; on the feast of St. Mary Magdalene, who was the first to believe the Resurrection, announced it to the Apostles, and thus became an Apostle to the Apostles; on the feasts of the holy Angels, because allusion is made to them, in these words: Maker of heaven and earth, and of all things visible and invisible; on the feasts of the Blessed Virgin, because the Credo also speaks of our Lady; (but it is omitted in Votive Masses). It is said also on the feast of the Dedication of a Church, and on Patronal Feasts, because it is supposed, that, on both those days, there will be a large concourse of people; and, it is on that account, that it is said on the Feast of St. John the Baptist, should it fall on a Sunday; for, otherwise, it is not said, because St. John came before the Mysteries were accomplished, and because there is no mention made of him in the Symbol. The Credo is said likewise when a Church possesses a large or important Relic of the Saint whose feast occurs, and on which, it is taken for granted, many Faithful will assist at the services.
The Symbol (=Creed) recited during the Mass is not that of the Apostles - it is that of Nicea; or, if we would speak with full precision, we should call it the Symbol of Nicea and Constantinople, inasmuch as the entire article referring to the Holy Ghost was added in the first Council of Constantinople against Macedonius.
Until the 11th century, the Credo was not thus publicly said in the Churches at Rome. St. Henry, Emperor of Germany, when visiting Rome, was surprised at not hearing the Credo during the Mass. He spoke on the subject to the then reigning Pontiff, Benedict the Eighth. The Pontiff told him, that the Church at Rome gave, in this, an indication of the purity of her faith, and that she had no need to express her rejection of errors, which had never been harboured within her walls. However, shortly after the Emperor’s remark, it was decided, that the Credo should be said in the Churches in Rome on Sundays; for that confession of faith would become all the more solemn, by its being promulgated from the very Chair of St. Peter.
The Nicene Symbol is longer than that of the Apostles, which, nevertheless, contains all the truths of faith; but, as heresies have gradually sprung up, it was found necessary to give further development to such
of the Articles as were attacked; and thus, the several heresies were pointedly condemned, each one as it appeared. This Symbol contains everything that we have to believe, for we say, in one of the articles: I believe the Church; and hence, by believing all that the holy Church believes, we possess everything that she has adopted, and everything she has declared to be the truth, in the Councils of Nicaea and Constantinople, as also in all the others which followed.
[Note: Among the various rubrical reforms that took place in 1960, the credo is now only recited on any feasts of the first class, first and second class feasts of the Blessed Virgin Mary and all feasts of the apostles. This elimination of various exceptional cases to rubrics, always for some mystical reason, was typical of the liturgical reforms that were taking place in the 20th century, even before the Second Vatican Council.]