Justin Holcomb has done the Church a favor in publishing two books: Know the Heretics and Know the Creeds and Councils. Both can serve as great introductions to the history of Christian theology, including both what Christians believe and why they believe it. I could see these books both being used in small group studies or read by lay Christians seeking to learn more about Christian belief.
First, Know the Heretics. This book begins with a discussion of what a “heresy” is. Such a discussion is important, as it often seems the only heresy nowadays is to call someone else a heretic. But if on one extreme there are those who would call nothing heresy, on the other are those who call everything heresy. Holcomb focuses in on only issues discussed in the great Christian creeds, such as the divinity and humanity of Jesus, the Trinity and so on. Thus, differing views on hell or on evolution or other secondary issues are not heresies.
From this he covers pretty much all the major heresies in the early church. Most of these arose from people trying to figure out and explain who Jesus was. So you have the heresy that Jesus was only human, as well as the heresy that Jesus was not human at all (Docetism). The most odd thing in this book is that it follows in chronological order until you get near the end. Holcomb covers the heresy of Eutychus (Monophystism) before covering that of Nestorius (Nestorianism), even though Nestorius’ controversy came first in history. So in the chapter on Eutychus, Holcomb has to allude to the story of Nestorius, which the reader has not come to yet. It reads a bit awkwardly and begs the question, Why not cover them in order?
The other book, Know the Creeds and Councils, is also good, though I found one flaw that bothered me. This book moves more beyond the early church, not just covering the early creeds but moving into councils from the Reformation era and even a few in the 20th century. Thus it is more broad, covering Catholic councils (Trent in the 1500s, Vatican II in the 1900s) and Reformed confessions (Westminster, Heidelberg Catechism). It is the absences in this broadness that makes me pause though. Why favor just these two traditions? During the Reformation era we are missing both Lutheran and Anabaptist writings. Or even move beyond mere belief and mention the Barmen Declaration that spoke out against Hitler in WWII.
Related to this, is what I see as perhaps an unavoidable problem in a book like this. In discussing the anathemas connected to one of the creeds, Holcomb reflects on whether one can be condemned for simply believing the wrong thing about God, as the creed states. Such a discussion is probably too deep for a book as brief as this and leads to more questions then answers. Are those who assent to the correct beliefs saved even if they commit horrific evils? Are some with questionable beliefs condemned to judgment even if they live as true disciples of Jesus? This is why I think something from Anabaptists (such as the Schleitheim Confession) and the Confessing Church in Germany would have filled out this book nicely.
That said, overall, these books are greatly helpful for any Christian.