Hieromartyr Irenaeus of Lyons (c. 130-202) was bishop of Lugdunum in Gaul, which is now Lyons, France. A Greek from Smyrna in Asia Minor, he was brought up in a Christian family, rather than converting as an adult, and this may help explain his strong sense of Orthodoxy.
In his Against Heresies, he lays out several statements of the Faith, in language that would soon be echoed by the third- or fourth-century Apostles' Creed. In Book 1, Chapter 10, he writes:
The Church, though dispersed through our the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: [She believes] in one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are 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 of God, and the advents, and the birth from a virgin, and the passion, and the resurrection from the dead, and the ascension into heaven in the flesh of the beloved Christ Jesus, our Lord, and His [future] manifestation from heaven in the glory of the Father “to gather all things in one,” and to raise up anew all flesh of the whole human race, in order that to Christ Jesus, our Lord, and God, and Saviour, and King, according to the will of the invisible Father, “every knee should bow, of things in heaven, and things in earth, and things under the earth, and that every tongue should confess” to Him, and that He should execute just judgment towards all; that He may send “spiritual wickednesses,” and the angels who transgressed and became apostates, together with the ungodly, and unrighteous, and wicked, and profane among men, into everlasting fire; but may, in the exercise of His grace, confer immortality on the righteous, and holy, and those who have kept His commandments, and have persevered in His love, some from the beginning [of their Christian course], and others from [the date of] their repentance, and may surround them with everlasting glory.
Later, in Book 3, Chapter 4, Irenaeus sums up the faith of the church, again emphasizing that the church uniquely holds the deposit of the faith, “since the apostles, like a rich man [depositing his money] in a bank, lodged in her hands most copiously all things pertaining to the truth: so that every man, whosoever will, can draw from her the water of life.”
To which course many nations of those barbarians who believe in Christ do assent, having salvation written in their hearts by the Spirit, without paper or ink, and, carefully preserving the ancient tradition, believing in one God, the Creator of heaven and earth, and all things therein, by means of Christ Jesus, the Son of God; who, because of His surpassing love towards His creation, condescended to be born of the virgin, He Himself uniting man through Himself to God, and having suffered under Pontius Pilate, and rising again, and having been received up in splendour, shall come in glory, the Saviour of those who are saved, and the Judge of those who are judged, and sending into eternal fire those who transform the truth, and despise His Father and His advent. Those who, in the absence of written documents, have believed this faith, are barbarians, so far as regards our language; but as regards doctrine, manner, and tenor of life, they are, because of faith, very wise indeed; and they do please God, ordering their conversation in all righteousness, chastity, and wisdom.
In the third and final place where Irenaeus writes a creedal statement, his emphasis is on the creedal statement as being the judge of who belongs to the church and who does not (Book 4, Chapter 33):
He shall also judge those who give rise to schisms, who are destitute of the love of God, and who look to their own special advantage rather than to the unity of the Church; and who for trifling reasons, or any kind of reason which occurs to them, cut in pieces and divide the great and glorious body of Christ, and so far as in them lies, [positively] destroy it,—men who prate of peace while they give rise to war, and do in truth strain out a gnat, but swallow a camel. For no reformation of so great importance can be effected by them, as will compensate for the mischief arising from their schism. He shall also judge all those who are beyond the pale of the truth, that is, who are outside the Church; but he himself shall be judged by no one. For to him all things are consistent: he has a full faith in one God Almighty, of whom are all things; and in the Son of God, Jesus Christ our Lord, by whom are all things, and in the dispensations connected with Him, by means of which the Son of God became man; and a firm belief in the Spirit of God, who furnishes us with a knowledge of the truth, and has set forth the dispensations of the Father and the Son, in virtue of which He dwells with every generation of men, according to the will of the Father.