Since the beginning of the Christian era, the term "canon" primarily refers to the normative rules of life and internal law. That is, the tradition that guided the first Christians, starting from the apostles. "Peace and mercy to all who follow this rule (κανόνι) - to the Israel of God", writes the apostle Paul in Gal 6. 16. Also in the epistle to the Philippians, he uses the word "canon" for the moral and legal norm, the rule of Christian life . In the works of the early Church Fathers the word κανών means "rule", "established norm". They also use it in relation to doctrinal (dogmatic) questions . The initial understanding of the canon in Christianity referred precisely to the conceptual area. It meant the ideas that reflect the norm of Christian morality and faith.
Later, "canon" starts to mean rather the administrative form of a list. This contrasts to the original meaning of the measure of truth, piety and Church tradition. Now canon is either a list of conciliar decisions, or a list of books of Holy Scripture, or a list of clerics of the diocese . So, already Saint Athanasius of Alexandria understands canon as "the correct list of divinely inspired books". (2nd rule of his 39th decree on holidays, c. 367). This is later repeated by St. Amphilochius of Iconium, Saint Augustine, Saint Jerome of Stridon and others .
When applied to the Biblical books, the word κανών can mean both "rule, norm, model", and "list". This administrative form of the list became the basis for what later developed into canon law. The canon law is a body of rules about ecclesiastical discipline. Thus, one can observe a change in the semantic paradigm that determines the understanding of the canon. For the early Christians canon was the measure of true life in Christ. Its basis was the unshakable dogmatic truth of Revelation, which was rather doctrinal in nature. Later, canon became the body of disciplinary law and the form of the list. This essentially differs from the original meaning. With this semantic turn the "canon of faith" in the singular turns into the plural. The "canons" as lists of rules appear.
As for the administrative significance of the canon as church law, it is important to understand its main task. It is to apply the eternal foundations of Christian moral teaching and dogmatic truths to the changing church life. "In any canon one can find the unchanging dogmatic teaching of the Church. But one can also find the conditions of a specific historical situation. These are the circumstances of church life as they were at the time the canon was issued. They could subsequently change"  . "The canons are not subject to repeal, but this does not mean that the legal norms established in them are absolutely unchanging" . Thus, it is important to clarify that there are two aspects in the understanding of the canon. First, there is the primary unchanging basis, conditioned by the dogmas. Second, there is the changeable tradition of applying this basis to the transient circumstances of church life.
With certain reservations, it can be said that the fine arts of the Middle Ages developed the so-called iconographic canon. It meant the artistic tradition of "the main compositional schemes and elements of depicting certain characters (their clothes, postures, gestures), landscape or architecture details" . In church musical art, the canon was one of the most complex forms of Byzantine hymnography (8th century). It consisted of nine songs, each having a certain structure. The first stanza (irmos) of each song was based on a plot from the Old Testament, and in the remaining stanzas (troparia) the themes of irmoi developed .