The New Testament presents early Christians as having a keen focus on sound teaching that builds us up into the most holy Faith. It will be obvious that the New Testament documents often do not state doctrine like a modern textbook, but its authors collectively contribute to something that we can recognize as the Faith, or better: the rule of faith.

Irenaeus’s On the Apostolic Preaching (c. 190) is the earliest extant non-polemical summary of Christian teaching that we know of (Behr, Preaching, 7). He wrote it to help a man named Marcianus understand the whole body of Christian teaching. As such, we can suppose it functioned as a catechesis document, aiming to help seekers and Christians alike know what the Faith once for all delivered was (Jude 3).

Three Features of On the Apostolic Preaching

What makes Irenaeus’s work worth reflecting on today are the following features. First, Irenaeus studied under Polycarp, who himself learned from the apostles. So Irenaeus has insight into part of the original audience of the New Testament documents, and he knew certain habits of mind that derive from the apostolic era.

Second, the work’s form follows patterns present in Acts (Behr, Preaching, 7). Irenaeus thus begins with Moses and all the prophets, showing how the Scriptures speak of Christ (cf. Luke 24:27). So we can see a work of ancient biblical theology that self-consciously aims to replicate apostolic patterns of scriptural interpretation.

Third, and related to this, Irenaeus calls the Old Testament Scripture, and he cites it primarily (not the New Testament) to establish the Faith. He obviously read the New Testament because he alludes to and cites it. But like the Apostolic Preaching in Acts, the Scriptures primarily refer to what we know as the Old Testament. None of these points means Irenaeus did not view the New Testament writings as authoritative, but rather that he, in imitation of the apostles, read Scripture to establish faith in Christ Jesus.

OT as Substructure for Apostolic Preaching

This approach might seem peculiar, yet I am convinced it is how we ought to approach the Scriptures through the apostolic writings. While I am not arguing this narrow point here, my judgment is that we often skip to the apostolic conclusions in the New Testament without understanding the Scriptural substructure of the Apostles. Irenaeus course-corrects us here, exposing at least one area where we typically lack sufficient knowledge.

Put simply, early Christians preached Christ according to Scripture primarily through the Old Testament while being guided by the Apostolic Writings (New Testament). Irenaeus shows us how second-century Christians did so in conscious imitation of the speeches of Acts and other New Testament writings.

John Behr explains Irenaeus’s intent in this way: “to relate the content of the apostolic preaching by outlining the history narrated in Scripture, culminating in the apostles’ proclamation that what is prophesied therein is now fulfilled in Jesus Christ, and thereby, in reverse, recognizing the scriptural authority of this preaching of the apostles” (Preaching, 16).

In other words, Irenaeus in his Demonstration of the Apostolic Preaching demonstrates how the Scriptures (Old Testament) establish the proclamation of the apostles. Or put differently, Irenaeus maintains that the apostles read the Old Testament in light of Christ, or Christ in accordance with Scripture.

Consider how the Apostle Paul puts it in 1 Corinthians 15:3–4: “I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures.”

As becomes clear in Paul’s letters, the way in which Paul reads Scripture is in a Christ-centric way. Christ is a main character, for example, during and after the Exodus when Moses struck the rock, which was Christ (1 Cor. 10:4). Jude 5 specifies that Jesus saved the people of Israel during the Exodus. And the preaching of the apostles regularly demonstrates their desire to show how Scripture anticipates Christ, who fulfills and proclaims the presence of the good promises of God.

Jesus evidently taught the Apostles this methodological approach to Scripture as Luke 24:27 implies: “And beginning with Moses and all the Prophets, he interpreted to them in all the Scriptures the things concerning himself.” One inference of this teaching may be that doctrine does not develop past the Scriptures and Christ’s proclamation, since the Christian faith centres on Christ as promised in the Scriptures (2 Tim. 3:16–17).

A second inference involves the source of the apostolic preaching and thus of the second-century church’s proclamation; Irenaeus locates that common source in the Old Testament Scriptures, not in Greek philosophy or other such thought. Put simply, the doctrine of the Trinity (and others) substantially existed in the apostolic writings themselves; and the later theological language applied revealed principles of unity and distinctness in God to a new problem (e.g., Arianism).

The Argument of On the Apostolic Preaching

Behr isolates “two integrated projects” that Irenaeus undertakes: first, to demonstrate or unfold the content of Scripture, the Old Testament, as it pertains to the revelation of Jesus Christ as preached by the apostles; second, “to recognize the scriptural authority of that preaching by demonstrating that the apostles’ proclamation of what has been fulfilled in Jesus Christ, shaped as it is by Scripture, was indeed so prophesied” (Preaching, 17).

He continues, “These two tasks are both conveyed by the one word which Irenaeus uses to describe this work—an ἐπίδειξις: a ‘demonstration’ both in the sense of an ‘exposition’ as well as a ‘proof.’ It is also in terms of these two projects that the text falls most naturally into two distinct parts” (Preaching, 17). Irenaeus first exposits the apostolic preaching (3b–42a) and then secondly demonstrates this teaching by scriptural citation (42b–97; Behr, Preaching, 18, 21).

In his introduction, Irenaeus says his work will “demonstrate, by means of a summary, the preaching of the truth, so as to strengthen your faith. We are sending you, as it were, a summary memorandum (κεφαλαιωδης ὑπόμνημα), so that you may find much in a little, and by means of this small [work] understand all the members of the body of the truth” (ch. 1).

The word demonstration (ἐπίδειξις), as Behr notes, indicates both exposition and proof, particularly of the teaching of the apostles.

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