"Of the dogmas and proclamations that are guarded in the Church, we hold some from the teaching of the Scriptures, and others we have received in mystery as the teachings of the tradition of the Apostles. Both hold the same power with respect to true religion. No one would deny these point, at least no one who has even a little experience of ecclesiastical institutions. For if we attempt to reject non-scriptural customs as insignificant, we would, unaware, lose the very vital parts of the Gospel, and even more, we would establish the proclamation merely in name. For instance—I will mention the first and most common—who has learned though the Scriptures that those who hope in the name of our Lord Jesus Christ are marked with the sign of the cross? What sort of scriptural text teaches us to turn to the East for prayer? Which saint has left us a scriptural account of the words of epiclesis at the manifestation of the bread of the Eucharist and the cup of blessing? We are not satisfied with the Eucharistic words that the Apostle or the Gospel mentions, but we add other words before and after theirs, since we have received non-scriptural teaching that these words have great power in regard to the mystery. We bless the water of baptism and the oil of chrism in addition to the very one who is to be baptized. By what Scriptures? Is it not by the secret and mystical tradition? But why? What scriptural authority teaches the anointing itself of oil? Where does a man being immersed three times come from? How much of the baptismal ritual is for the renunciation of Satan and his angels, and what scriptural text does it come from? Does it not come from this secret and unspoken tradition, which our fathers guarded with a simple and unprying silence, since they were well taught that the solemnity of the mysteries is preserved by silence? Such matters must not be seen by the uninitiated, and how is it appropriate that this teaching be published abroad in writing?
"In the same way, the Apostles and Fathers ordained from the first the matters of the Church and guarded the solemnity of the mysteries in secrecy and silence, for what is made known for a public and casual hearing is no mystery at all. This is the reason for non-scriptural traditions, that knowledge of dogmas not be neglected or despised by the many because of familiarity. For doctrine is one thing, and proclamation is another." On the Holy Spirit (27.66)