Review: Certainty for Life
Title: Certainty for Life: An Invitation to those in Eastern Orthodoxy
Author: John Diacos
Publisher: Ark House Press
Year: 2025
Reviewer: Mark Powell
Some books require a lifetime to write and Certainty for Lifeis one such example. Dr John Diacos, medical practitioner, former church planter and AFES (Australian Fellowship of Evangelical Students) worker in Melbourne has recently written an excellent book boldly challenging people from an Eastern Orthodox background with the truths of the biblical Gospel.
I have long thought that such a book needs to be written and here it finally is. There are already some well written Protestant critiques relating to Roman Catholicism, most notably Ray Galea’s Nothing in My Hand I Bring (Matthias Media, 2007). But to the best of my knowledge precious little has been produced relating to Eastern Orthodoxy.
Diacos himself grew up in the Eastern (Greek) Orthodox Church and so has an intimate understanding as to how people from this particular background view God, the Bible and salvation. Diacos is a gifted writer and there is a beautiful balance throughout the book of theological reflection, personal humour, exegetical insight, evangelistic zeal and practical illustration.
A scattering of personal testimonies can be found throughout the book. I thought that each of these was well-written and deeply moving. In some ways I wish there were more of them but that said, the book is long enough.
While I was studying at Moore Theological College in the 1990’s I attended a multi-cultural evangelical church made up predominantly of “ethnics” who had left the Orthodox church. The first two questions my wife and I were asked when we joined was, “How did you become a Christian?” and “What did your parents do in response?” This might sound like a strange question for many to hear, but it was a serious reality for people who had left Orthodoxy for evangelicalism. Just take, for example, the following extract from “Zachary’s Story” at the end of chapter ten:
During my early twenties, my father received a 4:30am telephone call from the father of a Greek friend of mine (who was studying medicine and reading the Bible with me). He told my father that if I ever contacted his son again, he would kill me. This demonstrated to me how evil some people can be, going to extreme measures to deny someone else exposure to the words of eternal life, as found in the Bible. This merely strengthened my resolve to devote my life to the sharing of the message for the Bible to others.
I especially appreciated how the book was structured in that Diacos deeply understands the Orthodox view of Scripture and Sacred Tradition as carrying equal authority. This is a key issue to address from the start since it clarifies whose voice one ultimately needs to listen to. While not denying its rightful ‘secondary’ place, Diacos warns of the danger tradition holds in nullifying the truth of God’s Word (i.e. Matt. 15:1-2). As Diacos explains:
As you read this book you will notice that, along the way, I incorporate several quotes from Church Fathers. I include these for their insightful and forceful reinforcement of the points we will see in the Bible. It also demonstrates that these are not new ideas, but were taught from the earliest days of Christianity. However, I have been selective. The reality is that I could easily produce a series of passages from the same, or equally respected, Church Fathers that make the completely opposite points. There is no uniformity in historical Christian doctrine. Traditions can be useful, but they cannot all be true. I do not think we have any difficult imagining this to be the case when we hear the variety of different beliefs being taught as Christian today.[1]
This is such an important point to clarify with people who are coming from an Orthodox background since they need to see that evangelical Christianity, rather than being a novel invention, is a return to the historically ‘orthodox’ Biblical position. As Gavin Ortlund rightly observed about Roman Catholicism, so many of its doctrines are—like barnacles on a ship—theological “accretions” which have metastasized over time and of which the early church Fathers knew nothing.
Central to Certainty for Life though, is its focus on one’s assurance relating to salvation. Diacos really does a masterful job here in clearly explaining the truth of the Gospel from the Scriptures. His explanation of sin, the atoning death and victorious resurrection of Jesus, as well as His high-priestly intercession for believers in heaven now are all presented in a clear and compelling way.
I was constantly struck throughout the book as to how Certainty for Life reads as a well-constructed sermon. Indeed, this is why I commented earlier that some books require a lifetime’s experience, reflection and reading to write. Diacos has thought about all the pertinent issues deeply and also how to compassionately persuade people who are Orthodox about why the differences are so significant.
The book concludes with a powerful challenge to take the claims of Christ seriously and to trust in Him alone for one’s salvation. All of which is to say, Certainty for Life is a book which I hope will—by the grace of God—have a profound and far-reaching impact. It is a book to buy, read and then give prayerfully away.
Diacos has produced an excellent resource for the church which helps evangelicals to further engage with people from an Orthodox background with the truth of the Gospel, Certainty for Life comes highly recommended.
[1] Diacos, Certainty for Life, 13.