Rule of Faith

The rule of faith (Latin: regula fidei) or analogy of faith (analogia fidei) is a phrase rooted in the Apostle Paul's admonition to the Christians in Rome in the Epistle to the Romans 12:6, which says, "We have different gifts, according to the grace given us. If a man's gift is prophesying, let him use it in proportion to his faith." (N.I.V.). The last phrase, "in proportion to his faith" is in Greek ἀναλογίαν τῆς πίστεως ("analogy of faith"). In Romans 12:6 this refers to one of three possible ideas: the body of Christian teachings, the person's belief and response to the grace of God, or to the type of faith that can move mountains. This phrase in Romans 12 becomes the root for later usage of the term by such Early Christian writers as Tertullian. Tertullian links it to the core set of Christian teachings, i.e.:

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 some 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" in On Prescription Against Heretics.

Although the term "rule of faith" is not used in them, passages in Irenaeus'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.