In a summary of the patristic notion of the regula fidei  in the Trinity Journal (2007), Paul Hartog helpfully stresses that the regulation of the regula was not only linguistic, doctrinal, dogmatic, or methodological. It had also to do with the reader’s disposition:

“Certainly hermeneutical methods were employed, and there were debates between the adherents of differing methods. But what was decisive was an attitude.2 The Christian interpreter does not approach Scripture with a tabula rasa. We believe in one God the Father Almighty, in one Christ Jesus, and in the Holy Spirit. If one approaches Scripture with the regulafidei in hand, then one approaches with faith in the heart. According to Irenaeus, the gnostics with their corrosive curiosity recited, ‘Seek and you will find,’ But the faithful knew that on a foundational level ‘the search has ended.’ Although the Hebrew Scriptures are a ‘treasure, hid indeed in a field,’ they have been ‘brought to light’ and ‘explained’ by the cross. Confession of Jesus as the Christ was the result of the kerygma and the presupposition of biblical interpretation. Irenaeus cautioned, ‘If you do not have faith, you will not understand.’”

Jenson again (Canon and Creed), on the mutual support of canon and creed:

“We cannot claim that the regula fidei actively shaped the very New Testament that came about. On the contrary, the material relation between the creedal tradition and the new canon is at first glance problematic. The creedal tradition provides little or no narrative of Christ’s teaching and deeds; it thus suggests, if anything, that the church could get along without it – which is to say, without Gospels. The creedal tradition, taken in itself, brings little theological reflection to the first article’s concept of creation, or to the events the second article narrates, or to the sanctifying contexts of which the third article tells us; thus it suggests, if anything, that the church could get along with such reflections as occupy Paul’s letters; the theological interpolations into the creed appropriated at Nicaea serve purposes other than those that creed served in its baptismal role.”

On the other hand, the church recognized that something was lacking, specifically, “those essential aspects of the message that the regula fidei did not – as our creeds still do not – directly support. One cannot, for example, forever keep saying, ‘Jesus died to save us from our sin,’ without pondering how that might work, without the kind of second-level reflection that Paul exemplifies. Thus sophisticated theological reflection a la Paul or the evangelist John belongs to the mission itself One cannot keep confessing, for example, ‘He is  Lord,’ without helpfully identifying the subject. Thus to remain gospel, the gospel narrative requires narrative expansion, a la the Gospels.”

Thus the canon and rule of faith fit like “conversely notched puzzle pieces.” The gospel could not be proclaimed except in summary; yet the gospel could not be fully proclaimed without elaboration in gospel narratives and in theological reflection. When they fit together, the “make one whole and integral guardian of the church’s temporal self-identity.”

According to Irenaeus (Against Heresies, 1.8.1), reading the Bible is like discerning a face among the fragments of a mosaic. Heretics read the Bible using sources other than Scripture and so the portrait they assemble is of a dog or fox. The orthodox arrive at a different arrangement:

The heretics’ “manner of acting is just as if one, when a beautiful image of a king has been constructed by some skilful artist out of precious jewels, should then take this likeness of the man all to pieces, should rearrange the gems, and so fit them together as to make them into the form of a dog or of a fox, and even that but poorly executed; and should then maintain and declare that this was the beautiful image of the king which the skilful artist constructed, pointing to the jewels which had been admirably fitted together by the first artist to form the image of the king, but have been with bad effect transferred by the latter one to the shape of a dog, and by thus exhibiting the jewels, should deceive the ignorant who had no conception what a king’s form was like, and persuade them that that miserable likeness of the fox was, in fact, the beautiful image of the king. In like manner do these persons patch together old wives’ fables, and then endeavour, by violently drawing away from their proper connection, words, expressions, and parables whenever found, to adapt the oracles of God to their baseless fictions. We have already stated how far they proceed in this way with respect to the interior of the Pleroma.”