The Eternal Son

by Robert Letham

Using an historical-theological approach supplemented by exegesis, Letham develops a biblically faithful Christology of the Son's deity, humanity, and incarnation, while examining major Christological heresies and creedal responses to them.

432 pages, Paperback

Published October 22, 2025

About the author

Robert Letham (MAR, ThM, Westminster Theological Seminary; PhD, Aberdeen University) is professor of systematic and historical theology at Union School of Theology in Bridgend, Wales, and the author of a number of books, including The Lord's Supper and Union with Christ.

Reviews

[Darren Lee · Rating 5 out of 5]

In contrast to Letham’s The Holy Trinity, I found The Eternal Son a much more engaging read. This book blends historical theology and systematic theology, with historical theology occupying a larger proportion. Some parts are admittedly dry, particularly the detailed patristic discussions, but even these sections are far less tedious than in The Holy Trinity. The historical discussions serve the systematic theology aim, introducing key concepts while Letham’s arguments remain firmly rooted in Scripture—both explicit statements and inferred reasoning—rather than relying solely on historical precedent. Notably, the focus here is on the person of Christ, rather than primarily on His work.

At times, the book’s detailed treatment of the patristic period, especially the events and debates before and after Chalcedon, felt dense and above my level. For me, the highlights lie in chapters 5–10, especially the treatment of figures such as Cyril, Maximus, John of Damascus, Aquinas, Luther, the Formula of Concord, Melanchthon, Calvin, Peter Vermigli, and Beza. Cyril emerges as a particularly central figure. I also appreciated how Letham clarifies Monophysitism in relation to Miaphysites and Eutychianism, which helped make sense of some of the historical controversies. Letham engages with modern theologians from the twentieth century onward, which further enriches the discussion.

I appreciate how Letham critiques both Lutheran and Reformed positions on the hypostatic union, even when he does not offer a definitive solution. As a Reformed theologian, he candidly acknowledges challenges in explaining how Christ’s flesh can be lifegiving without communication of attributes from His divine nature—a point that risks leaning toward Nestorianism—while also recognizing difficulties in the Lutheran approach.

However, I felt Letham missed the mark on Calvin’s autotheos issue, as he does not engage with the communication of essence, which I consider central. I also think it was a missed opportunity that he did not engage with EFS in this book, which would be very relevant to the current theological landscape. Minor issues include a missing page number for Zwingli’s reference on p. 222. The appendices (A and B) are less engaging and can be skipped without much loss. I also do not agree with his take that the Trinity is monarchial in a general sense; I still hold that the Father is the monarch of the Trinity. On a positive note, the glossary at the end is very helpful for navigating technical terms.

Some of the book’s key points that I found particularly insightful include:

• The error of conceiving two natures forming a person versus the orthodox view that a divine person assumes a human nature.

• Anselm’s explanation of why the Son, rather than the Father or Spirit, became incarnate (p. 70).

• Cyril’s Christology summarized (pp. 109, 299–300).

• The Theopaschite formula (p. 133).

• Distinction between gnomic will and natural will (p. 196).

• Dyothelitism is not gnomic (p. 183).

• The union of natures occurs in the person of the Son, not according to nature (p. 207).

• Aquinas’ three reasons why it is fitting for the Son to become incarnate (p. 209–210).

• Theandric activity and one agent acting according to two natures (p. 194, 198, 204, 274–275).

• Luther’s three modes of presence in the Eucharist (p. 220–221).

• Zwingli’s changed position on faith and the Eucharist (p. 222).

• Chemnitz’s threefold communication of attributes (p. 226).

• The state of humiliation in light of Lutheran views of the hypostatic union (p. 231).

• The concept of the incognito Christ (p. 276–277).

• Reflection on “whatever is not assumed cannot be healed” and its implications for Christ taking on fallen human nature (p. 283–285).

• Theosis/deification in relation to atonement, salvation, and cosmic renewal (p. 189, 301, final chapter). Cosmic renewal is really something new for me here.

Overall, I thoroughly enjoyed the book. It deepened my understanding of Christology while providing a rich engagement with both historical and systematic theological perspectives. I still have a lot to learn, especially regarding the finer details of historical theology!

[E · Rating 4 out of 5]

This is a work of historical theology. I did not know this at the time, but I'm glad for it. I've read other works of christology that focus on the systematics while including the historical; this book does the opposite. It is thus an excellent resource on the Constantinople, Chalcedon, and, importantly, post-Chalcedon. Letham makes a strong case that Chalcedon was not a final settlement, that important issues still needed to be resolved.

I do believe that Letham could have organized things a bit better, and the last five hundred years of things seemed rushed, or even quite rushed. But all the material here is solid, and orthodox. (And, like all of P&R academic works, very well edited. I assume Karen M had something to do with that.)