Early Christian thinkers carved out the contours of the faith—formulating doctrine, countering heresy, navigating differences between Eastern and Western traditions. For this, the church will ever be in their debt, owing much to their courage of conviction, fortitude of character, clarity of mind, and passion for truth. Irenaeus of Lyons, whose feast day is today, is one such figure.

Known as the “first great Catholic theologian,” Irenaeus traced his spiritual lineage directly back to the Apostle John, through Polycarp of Smyrna, under whose tutelage he sat as a child. This heritage uniquely poised Irenaeus for combatting the Gnosticism of his day, in that he could draw from both scripture and apostolic authority to delineate the essentials of the Christian faith. Irenaeus’ seminal work in this vein is Against Heresies, a masterful text consisting of five books that articulate Christianity’s basic doctrines, a proto-Mere Christianity if you will.

Gnosticism, the predominant heresy of the 2nd century church, promoted dualism, a doctrine wherein the material world was created and governed by the demiurge—a lesser creative being whom the Gnostics equated with Yahweh of the Old Testament—and Christ, as a representative from the spirit world governed by the supreme deity, offers human beings secret knowledge (gnosis) that makes possible man’s redemption. Contra Christian teaching, the Gnostics looked less to salvation from sin than to deliverance from the ignorance of which sin is a consequence. Against the Gnostics’ claim of exclusive knowledge about spiritual matters, Irenaeus proclaimed the universal availability of the gospel message; the good news is for all, and this good news runs throughout the whole of God’s special revelation.

In addition to Against Heresies, only one other of Irenaeus’ writings survives: The Proof of the Apostolic Preaching, a short work addressed to his friend Marcianus which serves as a primer to and an apologetic for the baptismal confession and Rule of Faith, forerunners to the Apostles’ Creed. The essay also establishes an important link between the Old Testament (OT) and the work of Christ, enumerating the many OT prophecies fulfilled by Christ and offering a holistic interpretation of both the Old and soon-to-be-established New Testament. For Irenaeus, God’s redemptive plan governs the entirety of scripture, a dominant theme in both of his extant works.

As J. Armitage Robinson has noted, “The wonder of Irenaeus is the largeness of his outlook. No theologian had arisen since St. Paul and St. John who had grasped so much of the purpose of God for His world.” In explaining and defending the Apostolic message, Irenaeus traces God’s salvific purpose through scripture—revealing the organic connections between Christianity and its Jewish heritage, the fall of Adam and the resurrection of Jesus, the giving of the Law and the offer of grace, creation and the eschaton, along the way fitting key biblical figures within that story.

For two millennia the creed has been an anchor keeping us moored to the word and the Word.

The aforementioned Rule of Faith, which functioned so centrally in The Proof of the Apostolic Preaching, affirms belief “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.”

A slightly different version, the Old Roman Creed, reads as follows:

I believe in God the Father almighty; and in Christ Jesus His only Son, our Lord, Who was born from the Holy Spirit and the Virgin Mary, Who under Pontius Pilate was crucified and buried, on the third day rose again from the dead, ascended to heaven, sits at the right hand of the Father, whence He will come to judge the living and the dead; and in the Holy Spirit, the holy Church, the remission of sins, the resurrection of the flesh (the life everlasting).

For 2,000 years Christians have joined this refrain, week after week adding their voices, reaffirming its life-giving truths. For two millennia the creed has been an anchor keeping us moored to the word and the Word.

In this world of change and flux, and amidst the vicissitudes, variables, and vagaries of life, so invariant a creed has remained a constant, a stable shore at the edge of a sea’s worth of maelstroms featuring the howling winds and shifting sands of unsound doctrines. Such seems Irenaeus’ motivation for explaining and defending it so many years ago, as he admonishes Marcianus: “Wherefore it is needful for you and for all who care for their own salvation to make your course unswerving, firm and sure by means of faith, that you falter not, nor be retarded and detained in material desires, nor turn aside and wander from the right.”

Perhaps at such a time as this, in the hour in which we find ourselves, when the church feels under siege from multiple directions, various of its classical commitments disparaged and impugned by some, castigated as outdated and archaic by others, Irenaeus serves as a powerful reminder to walk in the way of righteousness, stand on the bedrock of orthodoxy, keeping our eyes on the Author and Finisher of our faith, focusing on what can draw us together as believers rather than on what so easily divides, and, most importantly of all, encouraging fidelity to Christ and faithfulness to His mission amidst the deafening din of a cacophony of voices as we serve the God who is the same yesterday, today, and forever.