Irenaeus’s Against Heresies, but Just the Best Parts!

By Derek DeMars on January 28, 2022 • ( 0 )

In some earlier posts I mentioned my recent fascination with the theological writings of Saint Irenaeus of Lyons, whose massive book Against Heresies is one of the most important works of ancient Christian theology.

Obviously I personally got a lot of fulfillment from reading it, and I’d love for more people to check it out for themselves. But unfortunately this five-volume, 600-page, densely-worded treatise is certainly not for the faint of heart. In fact, I think it should come with a warning label!

Against Heresies divides into five “books” or parts, and the first two are incredibly dense and difficult to get through.

This is because, in those first two books, Irenaeus sets out at length the full teachings of the prominent Gnostic leaders so that his readers could see for themselves how convoluted and bizarre they were. It’s chapter after chapter of the names of various Gnostic Aeons and their made-up relation to each other, among other oddities.

There are some worthwhile observations from Irenaeus along the way, but finding them is a bit like digging for buried treasure.

In the three latter books, Irenaeus thankfully shifts his focus more toward explaining true Christian doctrine and how the Gnostic errors are refuted by Scripture and plain common sense, so the book begins to be more readable. And yet, even they contain many sections where some of the reasoning is a bit obtuse or else simply not as relevant since we’re no longer dealing with the same claims from Gnostic opponents.

That said, I’m here to help! I’ve done the heavy lifting so you don’t have to!

In the rest of this post, I’m going to list those portions of St. Irenaeus’s Against Heresies that I think are the most essential reading, and the topics they cover, so that you can skip straight to the meat of the book.

Against Heresies can be read in its entirety in English online (here’s a link), or if you prefer a print copy I really like this edition put out by Ex Fontibus. Also, note that each of the five books are divided into chapters, and those chapters have numbered subsections. I’ve put links to all the references below, so you can click the chapter numbers to go straight to the reading.

Without further ado, here are the most essential sections of Against Heresies that you should read:

Book I:

Read the Preface, and consider skimming the first two or three chapters to get an idea of the convoluted mess that is Gnosticism, to which Irenaeus was responding. Then jump ahead to chapter 6 to get an idea of the heretics’ practices. Next read 8.1 for Irenaeus’s clever analogy of a broken mosaic to describe false teaching.

Chapter 10 is very important to read, as Irenaeus introduces one of his chief arguments against the diverse Gnostic sects – namely, the fact of the unity of the true Church and its teaching encapsulated in the rule of faith (a precursor to the later creeds).

Check out 21.1 and notice Irenaeus’s description of baptism as the means or occasion of regeneration, read 22 for more on the rule of faith, and check 26 and 27 for a brief rundown of some of the more interesting heretical sects like Marcionism.

Book II:

Chapter 2 offers an interesting glimpse of Irenaeus’s doctrine of creation. In 13.3-4 Irenaeus comments on the nature of God and divine simplicity. 20.3 has some comments on Christ’s atoning work. 22.4 contains an implicit affirmation of infant baptism, in that he says infants can be “born again to God.”

Chapters 26, 27, and 28 are all worth reading, as they contain some beautiful reflections on the limits of human knowledge and the need for careful, faithful interpretation of Scripture.

29.2 is a good comment on the future bodily resurrection and God’s goodness. Chapter 30 discusses angels, for those interested, and culminates in an important early affirmation of Christ’s co-eternality with the Father.

In 32.1 Irenaeus points out how Christ’s teaching overturns any kind of moral relativism (an observation still relevant today). And in 32.4 he describes the presence of charismatic gifts and miracles still occurring among the second-century church.

In 33 and 34 he argues against belief in reincarnation. It’s pretty technical, so only read if you’re interested in that.

Book III:

Definitely read chapters 1-5, one of the most important sections of the whole work, where he teaches on the nature of Christian orthodoxy, affirms the primacy of Scripture and then apostolic tradition as authorities for true doctrine, points out the unity of the true faith throughout the whole world in the catholic (i.e. universal) Church, and documents the succession of orthodox tradition from the apostles down through the bishops and presbyters of the Church.

In 9.3 he affirms Christ’s full humanity and full divinity. Read chapter 16 for even more reflections on how the four Gospels affirm Christ’s full divinity and the meaning of his incarnation.

Chapters 18 (especially 18.6-7) and 19 contain some of Irenaeus’s most profound reflections on the saving work of Christ. 20.2 is likewise important – Irenaeus ventures a theory as to why God allowed the world to become broken in the first place.

Chapter 22 discusses the virgin birth, for those interested. In 23 Irenaeus gives a fascinating argument for why he believes Adam will be saved (and why he thinks that’s important).

24.1 is a strong statement on the importance of being part of the Church. And 25 has some good reflections on God’s goodness and justice, and closes with Irenaeus’s prayer that the heretics will repent of their error.

Book IV:

The preface is a good summary of the previous material. Chapter 2 affirms the inspiration of the Old Testament and the role of messianic prophecy. In 6 Irenaeus explains what it means that “No one knows the Father except the Son and anyone to whom the Son chooses to reveal him,” and how that fits with the universal offer of the gospel.

Chapters 8-18 discuss the relationship between the Old and New Testaments, the role of the Law of Moses, messianic prophecy, and why Christianity cannot jettison the Old Testament. Lots of great material for the patient reader to chew on. In 17.5-6 and 18, he touches on the offerings of the Church and particularly the Eucharist – very important.

Chapter 20 discusses Christ as the Wisdom of God and what it means to see God (20.5-7 is an especially stirring and memorable passage about how “the pure in heart shall see God” and the glorification of believers). And 26 explains how Christ is at the center of Scripture, and the importance of having good presbyters in the Church to teach this true faith.

In 29 he discusses the hardening of Pharaoh. 33 covers the future Second Coming and final judgment, and the need to remain united to the true faith of the Church. 36.2 features a lovely allegory where Irenaeus uses the Parable of the Vineyard to summarize the whole biblical storyline.

Chapters 37-39 are very important for understanding Irenaeus’s theology. In 37 he vigorously affirms humanity’s free will. Then in 38 he explains his thoughts on why God has allowed evil. And in 39 he affirms that God carries out his predetermined plan while taking account of his foreknowledge of creaturely choices.

And finally in 41 he explains the fall of the devil, evil angels, and humanity.

Book V:

Chapters 1 and 2 discuss how Christ’s death in the flesh secures our salvation, and how this is reflected in the Eucharist. Chapters 8-9 discuss Christian spiritual growth by the power of the Holy Spirit and the future salvation of our whole humanity in the resurrection.

15.3 has another reference to baptismal regeneration. 21 summarizes Christ’s victory over Satan. In 23.2 Irenaeus mentions that believers had several theories as to what it meant that Adam and Eve would die “on the very day” they ate the forbidden fruit.

In 25-31 Irenaeus discusses end times, including his belief in a future Antichrist and tribulation culminating in the resurrection and the millennial kingdom. And in 32-36 he concludes by arguing for belief in a literal thousand-year reign of Christ before the final new heavens and new earth.