Prior to Nicea, each church had their own rule of faith (though all were very similar), which contained the central tenets of Christianity memorized at baptism by all new Christians.
Let us give up purposeless and fruitless cares and approach the holy and venerable rule of our calling. Let us attend to what is good, pleasing, and acceptable in the sight of him who formed us. Let us look steadfastly to the blood of Christ and see how precious that blood is to God, which has set the grace of repentance before the whole world. Let us turn to every age that has passed and learn that … the Lord has granted a place of repentance to all that would be converted to him. Noah preached repentance, and as many as listened to him were saved. (First Clement 7)
The one who retains the rule of the truth received through baptism unchangeable in his heart will surely recognize the names, the expressions, and the parables taken from the Scriptures [by the gnostics] but will by no means acknowledge the blasphemous use which these men make of them. (Against Heresies I:9:4)
The church, though dispersed throughout the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith in one God the Father Almighty, Maker of heaven, earth, and the sea and everything in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit, who proclaimed through the prophets the dispensations, the advents, the birth from a virgin, the suffering, the resurrection from the dead, and the ascension into heaven in the flesh of the beloved Christ Jesus, our Lord, and his appearance from heaven in the glory of the Father to gather all things into one and to raise up anew all flesh of the whole human race, in order that every knee should bow—of things in heaven, things in earth, and things under the earth—and that every tongue should confess to him, and that he should execute just judgment towards everyone; that he may send spiritual wickednesses and the angels who transgressed and became apostates together with the ungodly, unrighteous, wicked, and profane among men into everlasting fire, but may, in the exercise of his grace, confer immortality on the righteous, holy, and those who have kept his commandments and persevered in his love—some from the beginning of their course and others from their repentance—and may surround them with everlasting glory. (Against Heresies I:10:1)
Such spirits as are commanded by [the gnostic heretics] and speak when they desire it, are earthly and weak … sent forth by satan for the seduction and perdition of those who do not hold fast that well-compacted faith which they received at first through the Church. (Against Heresies I:13:4)
Rainbow over Jackson, Tn
The rule of truth which we hold is that there is one God Almighty who made all things by his Word and fashioned and formed—out of that which had no existence—all things which exist. … Holding this rule we shall easily show that [the gnostics] have deviated from the truth, no matter how many opinions they have nor how much they vary. For almost all the different sects of the heretics admit there is one God, but then, by their pernicious doctrines, they shift, just like the Gentiles do through idolatry. (Against Heresies I:22:1)
A sound mind—one which does not expose its possessor to danger and is devoted to piety and the love of truth—will eagerly meditate on those things which God has placed within the power of mankind and has subjected to our knowledge … which makes knowing those things easy by mean of daily study. These things are those that can be seen by us and are clearly, unambiguously, and directly set forth in the Scriptures. However, if you use expressions which are not clear and evident in the interpretations of the parables, the kind everyone finds as their fancy leads them, then no one will have the rule of truth. Instead, however many people explain the parables will be how many differing systems of truth there are! They will be opposed to each other and teaching competing doctrines, such as is typical among the Gentile philosophers. (Against Heresies II:27:1)
Since we have the truth itself, set plainly in front of us, as our rule and testimony concerning God, we ought not to cast away the firm and true knowledge of God and run after numerous and various answers to questions. (Against Heresies II:28:1)
The disciple of the Lord [elsewhere said by Irenaeus to be the apostle John] wanted to put an end to all [the gnostic] doctrines and to establish the rule of truth in the church: namely, that there is one Almighty God, who created all things by his Word … by the Word he also bestowed salvation on the men included in the creation. To establish this, he began his teaching in the Gospel with: "In the beginning was the Word, and the Word was with God, and the Word was God. ( Against Heresies III:11:1)
Some of these [gnostics] impudently assert that the apostles, when preaching to the Jews, could not declare another god to them except the one in whom they believed. We tell them that if the apostles used to speak to people in line with the opinions instilled in those people in the past, then no one learned the truth from them. And before them no one learned the truth from the Lord, for they say he spoke the same way. In fact, these men can't know the truth, either. The opinion they have now is simply the teaching they received as they were able to hear it. If all this is true, then the rule of truth is with no one. … The coming of the Lord was apparently useless and unnecessary if he came just to tolerate and preserve each person's idea about God that they had received in the past. (Against Heresies III:12:6)
We follow the one and only true God as our Teacher. We possess his words as the rule of truth. We all speak alike and about the same things. We know but one God, the Creator of this universe, who sent the prophets, led forth the people from the land of Egypt, and who in these last times has manifested his own Son so that he might put unbelievers to confusion and search out the fruit of righteousness. (Against Heresies IV:35:4)
Whatever you do, do all to the glory of God; that is, what you are commanded to do by the rule of faith. [Here Clement is not speaking of a statement of faith or any doctrines, he means your deeds as "ruled" or "measured" by faith in Christ. I include this as a picture that "rule of faith" is not always a set of doctrines learned at baptism.] (Miscellanies IV:15)
"All things are right," says the Scripture, "to those who understand." That is, those who receive and observe, according to the rule of the Church, the exposition of the Scripture explained by [Christ]. And the rule of the Church is is the concord and harmony of the Law and the Prophets in the covenant delivered at the coming of the Lord. (Miscellanies VI:15)
As the work [Clement's book, Miscellanies] advances, we shall in each section note the figures of speech mentioned above by the prophet [i.e., Solomon in Proverbs] … explaining it systematically according to the rule of the truth. Did not the Power that appeared to Hermas in the Vision [i.e., The Shepherd of Hermas, a mid 2nd-century work] in the form of the Church give him a book for transcription that she wanted the elect to know about? This book, he says, he transcribed to the letter, without finding how to complete the syllables. This signified that the Scripture is clear to all when taken according to the bare reading and that this is the faith that occupies the place of the basics. …
Further, Isaiah the prophet is ordered to take a new book and write in it certain things. The Spirit of God was prophesying that through the Scriptures there would later come the sacred knowledge, which was at that time still unwritten, because it was not yet known. For it was spoken in the beginning only to those who understand. Now it has been handed down to us that the Saviour taught the apostles the unwritten rendering of the written Scriptures, inscribed by the power of God on new hearts, as the new book indicates. ( Miscellanies VI:15)
When we are going to enter the water, but a little before, in the presence of the congregation and under the hand of the president, we solemnly profess that we disown the devil, and his pomp, and his angels. Hereupon we are thrice immersed, making a somewhat ampler pledge than the Lord has appointed in the Gospel. (De Corona 3)
That this rule of faith has come down to us from the beginning of the gospel, even before any of the older heretics, much more before Praxeas, a pretender of yesterday, will be apparent both from the lateness of date which marks all heresies, and also from the absolutely novel character of our new-fangled Praxeas. In this principle also we must henceforth find a presumption of equal force against all heresies whatsoever: that whatever is first is true, whereas that is spurious which is later in date. (Against Praxeas 2)
All the Scriptures attest the clear existence of, and distinction in, (the Persons of) the Trinity, and indeed furnish us with our Rule of faith. (Against Praxeas 11)
No man receives illumination from an area where all is darkness. Let our seeking, therefore, be in that which is our own, 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. (Prescription Against Heretics 12)
Now, with regard to this rule of faith, so that we may acknowledge from this point on what it is we defend, it is, you must know, that which prescribes the belief that there is only one God, and that he is none other than the Creator of the world, who produced all things out of nothing through his own Word, the very first One sent forth. This Word is called his Son, and under the name of God [he] was seen in various ways by the patriarchs, heard at all times in the prophets, and at last brought down by the Spirit and power of the Father into the virgin Mary. [He] was made flesh in her womb and, being born of her, went forth as Jesus the Christ. From then on he preached the new law [Heb. 7:12] and the new promise of the kingdom of heaven and worked miracles. Having been crucified, he rose again the third day. Having ascended into the heavens, he sat at the right hand of the Father. In his place he sent the power of the Holy Spirit to lead those who believe. [He] will come with glory to take the saints to the enjoyment of everlasting life and of the heavenly promises and to condemn the wicked to everlasting fire once the resurrection of both these classes shall have happened, together with the restoration of their flesh.
This rule, as it will be proved, was taught by Christ and raises among ourselves no other questions than those which heresies introduce and which make men heretics.(Prescription Against Heretics 13)
So long … as the form [of the rule of faith] exists in its proper order, you may seek and discuss as much as you please. [You may] give full reign to your curiosity in whatever seems to hang in doubt or to be shrouded in obscurity. (Prescription Against Heretics 14)
Surely you have a teacher around that is gifted with the grace of knowledge. [You have] someone of the experienced class, someone you're closely acquainted with who is curious like yourself. Although he is a seeker like you, he will be quite aware, you newest of novices, that it is better for you to remain in ignorance, lest you should come to know that which you ought not. For you have already acquired the knowledge of what you ought to know [i.e., in the rule of faith].
"Your faith," he says, "has saved you," not your skill in the Scriptures. Now, faith has been deposited in the rule [of faith]. It has a law, and—in the observance of it—salvation.
Skill [in the Scriptures] consists in curious art. Its glory is simply the readiness that comes from study. Let such curious art give place to faith, and let such glory yield to salvation. ( Prescription Against Heretics 14 & 15)
From what and through whom and from when and to whom has been handed down that rule by which men become Christians? For wherever it is apparent that the true Christian rule and faith shall be, there will likewise be the true Scriptures and expositions thereof and all the Christian traditions. (Prescription Against Heretics 19)
From this, therefore, do we draw up our rule. Since the Lord Jesus Christ sent the apostles to preach, no others ought to be received as preachers than those whom Christ appointed … Nor does the Son seem to have revealed [the Father] to any other than the apostles, whom he sent forth to preach … What that was which they preached … can … properly be proven in no other way than by those very churches which the apostles founded in person, by declaring the Gospel directly to them themselves, both viva voce, as the phrase is, and afterwards by their letters.
If, then, these things are so, it is equally apparent that all doctrine which agrees with the apostolic churches, those molds and original sources of the faith, must be reckoned for truth, as undoubtedly containing that which the churches received from the apostles, the apostles from Christ, and Christ from God. In the same way, all doctrine must be prejudged as false which savors of disagreement with the truth of the church and apostles of Christ and God. …
We have fellowship with the apostolic churches because our doctrine is not in any way different from theirs. This is our witness of truth. (Prescription Against Heretics 21)
Nevertheless, through the whole Scripture is the rule of truth ; and whatever is ther delivered is infallibly true ; yet because there is contained in those writings great variety of things, and many occasional doctrines and decisions of controversies, which though all equally true, yet are not all equally necessary to be known and understood by all Christians of all capacitites ; therefore the Church from the beginning has out of the Scripture selected those plain fundamental doctrines, which were there delivered as the terms or conditions of Salvation, of necessity to be known and understood by all Christians whatsoever. And these, all persons were taught in their Baptismal Creeds. (The Scripture-Doctrine of the Trinity. [London] 1719. p.vi-vii)
For, matters of speculation indeed, of philosophy, or art ; things of human invention, experience or disquisition ; improve generally from small beginnings, to greater and greater certainty, and arrive at perfection by degrees ; but matters of Revelation and divine testimony, are on the contrary complete at first ; and Christian Religion, was most perfect at the beginning ... In the days of the Apostles therefore, christianity (sic) was perfect. (The Scripture-Doctrine of the Trinity. [London] 1719. p.vi-vii)
This is the rule of faith presented to the Council of Nicea by Eusebius the historian, overseer of the church at Caesarea. It was used as the basis for the Nicene Creed. The Council adjusted the creed to cover the subject of homoousios or "one substance."
We believe in one God, the Father Almighty, Maker of all things visible and invisible;
And in one Lord, Jesus Christ, the Word of God; God of God, Light of light, Life of life; the only-begotten Son, born before all creation, begotten of God the Father before all ages, by whom also all things were made; who on account of our salvation be- came incarnate and lived among men; and who suffered and rose again on the third day, ascended to the Father, and shall come again in glory to judge the living and the dead.
We believe also in one Holy Spirit.
We believe in the existence and subsistence of each of these: that the Father is truly Father, the Son truly Son, and the Holy Spirit truly Holy Spirit; even as our Lord also, when he sent his disciples out to preach the Gospel, said, "Go and make disciples of all nations, baptizing them in the name of the Father, of the Son, and of the Holy Spirit" [Matt. 28:19-20]. (The Ecclesiastical History of Socrates Scholasticus I:8)
The Nicene Creed represents the first universal rule of faith. Prior to Nicea, each church had its own rule of faith. Though they were all very similar, representing the faith delivered to the churches by the apostles, there was not a formalized, mandatory creed until the Nicene Creed. It did not gain wide acceptance until the emperor Theodosius finally vanquished the supporters of Arius in A.D. 383. It has represented the basic rule of faith for almost every church or denomination since. The Apostles Creed is simply a slightly expanded version of the Nicene Creed.
We believe in one God, the Father Almighty, Maker of all things visible and invisible.
And [we believe] in one Lord Jesus Christ, the Son of God, the only-begotten of the Father. That is, of the substance of the Father; God of God and Light of light; true God of true God; begotten, not made, consubstan- tial with the Father. By [him] all things were made, both which are in heaven and on earth: who, for the sake of us men and on account of our sal- vation, descended, became incarnate, and was made man; suffered, arose again the third day, and ascended into the heavens, and will come again to judge the living and the dead.
[We] also [believe] in the Holy Spirit.
But the holy, catholic, and apostolic church anathematizes those who say, "There was a time when he was not" and "He was not before he was begotten" and "He was made from that which did not exist," and those who assert that he is of other substance or essence than the Father, that he was created, or is susceptible of change. (The Ecclesiastical History of Socrates Scholasticus I:8)
Appeals to "the word of truth," "apostolic teaching," "tradition," "sound doctrine," and "thefaith" continued into the second century as an appeal to the Rule of Faith. The Rule of Faith was used in the early church as a standard against which all teaching was measured. … even the Christian writings eventually included in the New Testament canon were subjected to this Rule of Faith. (A High View of Scripture?, from the Evangelical Ressourcement series. Baker Academic, 2007, p. 55)