Let our "seeking," therefore be in that which is our own, and from those who are our own, and concerning that which is our own, - that, and only that, which can become an object of inquiry without impairing the rule of faith.
The rule of faith is the name given to the ultimate authority or standard in religious belief, such as the Bible alone, as among Protestants; the Bible and tradition, as among Catholics; reason alone, as among rationalists; as among the Eastern Orthodox it is theoria the inner light of the spirit, as among mystics.
The word "rule" actually only shows up once in the Christian New Testament at Galatians 6:16 in the following passage:
May I never boast of anything except the cross of our Lord Jesus Christ, by which the world has been crucified to me, and I to the world. For neither circumcision nor uncircumcision is anything; but a new creation is everything! As for those who will follow this rule (κανόνι) — peace be upon them, and mercy, and upon the Israel of God. (Gal 6:14-16, NRSV Anglicized Version)
Paul is using the word in a fairly occasional sense here, hence follow this rule. As noted, some 120 years after Paul, Tertullian uses the phrase "rule of faith," and reading this in its On Prescription Against Heretics context will at least lead you to the meaning Tertullian was giving the phrase.
Although the term "rule of faith" is not used in them, passages in Ireneus's Against Heresies such as Book 1.1.1, or Book 3.2.2 are examples of the concept, both describing the Christian fundamental beliefs and also emphasizing the importance of being united to apostolic teachings versus all others.
In Christian theology, it is a principle which evaluates religious life and theological opinions by testing them for consistency against what has been firmly believed. The original rule of faith in the Early Christian Church as Irenaeus knew it, included the following:
- … this faith: in one God, the Father Almighty, who made the heaven and the earth and the seas and all the things that are in them; and in one Christ Jesus, the Son of God, who was made flesh for our salvation; and in the Holy Spirit, who made known through the prophets the plan of salvation, and the coming, and the birth from a virgin, and the passion, and the resurrection from the dead, and the bodily ascension into heaven of the beloved Christ Jesus, our Lord, and his future appearing from heaven in the glory of the Father to sum up all things and to raise anew all flesh of the whole human race … :
In the Roman Catholic Church, the Bible and Sacred Tradition (that is, things believed to have been taught by Jesus and the apostles that were not recorded in the Bible but were transmitted through the church) are considered a rule for all believers for judging faith and practice.
In conservative Protestantism Romans 12:6 is viewed as the biblical reference for the term "analogy of the faith" (i.e., αναλογἰα τῆς πἰστεως). The Bible alone is considered the word of God and the only infallible standard for judging faith and practice; hence, for conservative Protestantism, the analogy of the faith is equivalent to the analogy of scripture – that is, opinions are tested for their consistency with scripture, and scripture is interpreted by the Holy Spirit speaking in scripture (compare sola scriptura).
The analogy of faith, which was advanced by St. Augustine, is sometimes contrasted with the analogy of being (Latin: analogia entis), which, according to St. Thomas Aquinas, allows one to know God through analogy with his creation.
- ↑ Tertullian, On Prescription Against Heretics, 12: see also chapter 13: Ante-Nicene Fathers, vol. 3, eds. Roberts and Donaldson, 1976, p. 249
- ↑ "The Rule of Faith". Catholic Encyclopedia. http://www.newadvent.org/cathen/05766b.htm. Retrieved 2007-02-18.
- ↑ CHURCH SYNODS AND CIVILISATION by John S. Romanides e) Theology and dogma. All who have reached glorification testify to the fact that "it is impossible to express God and even more impossible to conceive Him" because they know by their experience that there is no similarity whatsoever between the created and the uncreated. God is "unmoved mover" and "moved" and "neither one". Nor oneness nor unity,. nor divinity... nor sonship, nor fatherhood, etc." In the experience of glorification. The Bible and dogmas are guides to and abolished during glorification. They are not ends in themselves and have nothing to do with metaphysics, either with analogia entis or with analogia fidei. This means that words and concepts which do not contradict the experience of glorification and which lead to purification and illumination of the heart and glorification are Orthodox. Words and concepts which contradict glorification and lead away from cure and perfection in Christ are heretical. This is the key to the decisions of all Seven Roman Ecumenical Councils as well as that of the Eighth of 879 and especially of the Ninth of 1341. Most historians of dogma do not see this because they believe the Fathers were, like Augustine, searching by meditation and contemplation to understand the mystery of God behind words and concepts about Him. They induct even such Fathers as Gregory the Theologian into the army of Latin theology by translating him to say that to philosophise about God is permitted only to "past masters of meditation," instead of "to those who have passed into theoria", which is vision of Christ "in a mirror dimly", by "kinds of tongues" and "face to face" in "glorification". The Fathers never understood the formulation of dogma as part of an effort to intellectually understand the mystery of God and the incarnation. St. Gregory the Theologian ridicules such heretics: "Do tell me, he says, what is the unbegottenness of the Father, and I will explain to you the physiology of the generation of the Son and the procession of the Spirit, and we shall both of us be frenzy-stricken for prying into the mystery of God". Neither did the Fathers ever entertain the Augustinian notion that the Church understands the faith better with the passage of time. Every glorification is a participation in all the Truth of Pentecost, which can neither be added to nor better understood. This also means that Orthodox doctrine is purely pastoral since it does not exist outside the context of the cure of individual and social ills and perfection. Being a theologian is first and foremost to be a specialist in the ways of the Devil. Illumination and especially glorification convey the charisma of the discernment of spirits for outwitting the Devil, especially when he resorts to teaching theology and spirituality to those slipping from his grip. 
- ↑ "Regula Fidei" The New Schaff-Herzog Encyclopedia of Religious Knowledge, Vol. IX: Petri - Reuchlin
- ↑ "Roman Catholic Doctrine Concerning the Rule of Faith", chapter 5 of the introduction to Charles Hodge's Systematic Theology
- ↑ Catechism of the Catholic Church Sec.1, Chapter 2, Art. 3 SACRED SCRIPTURE, III. THE HOLY SPIRIT, INTERPRETER OF SCRIPTURE, esp. 114.3
- ↑ "Biblical Theology and the Analogy of Faith". Daniel Fuller. http://documents.fuller.edu/ministry/berean/analogy.htm. Retrieved 2009-03-08. ; John Calvin, Institutes of the Christian Religion [Prefratory Address, 2 and Book IV, ch. 17, 32], John T. McNeill, ed., Library of Christian Classics, 2 vols. (Philadelphia:Westminster Press, 1950), 1:12; 2:1404.
- ↑ "The Protestant Rule of Faith", chapter 6 of the introduction to Charles Hodge's Systematic Theology
- ↑ Introduction to Nature and Grace: Selections from the Summa Theologica of Thomas Aquinas, Philadelphia: The Westminster Press, 1954, p. 28.