This review will be a little longer as I explain how some parts influenced me in my move to Anglicanism (of which McGrath belongs as well).
This book was assigned to me for my Historical Theology class at Moody Bible Institute Chicago. There are four sections to this book which are divided by time periods: 1) Patristic (100-451 A.D.) 2) Middle Ages and Renaissance (500-1500 A.D.) 3) Reformation and Post-Reformation (1500-1750) 4) Modern Period (1750-Present). I covered the first three sections in class and then the fourth section on my own many months later.
Historical theology is the study of how theology develops over time. In each section McGrath covers 1) an overview of that time period 2) the key theological developments of that time 3) key theologians 3) key names/words/phrases. Finally, he does various case studies of that era such as the Nestorian controvesy of the Patristic, Aquinas' arguments for the existence of God in the Middle Ages, the debate over infant baptism in the reformation period, and the quests for the historical Jesus in the modern period.
The three things that influenced me the most in this book were:
1) The emphasis on the outward unity of the church and how schism was viewed as a serious sin in the Patristic period (most notably condemned by Cyprian of Carthage). I can't help it that I was born into a fractured church, but I can make the decision today to either be part of the body that has a record of schisms over non-essentials or to be part of a body that works towards healing those breaks (ecumenical relationships that led to full communion). Being against schism and for unity is what led me to Anglicanism.
2) The justification controversy at the Council of Trent was an eye-opener for me as I had never heard the perspective that McGrath shared. He said that the condemnation of justification by faith alone was a semantics issue. Roman Catholics did not view justification like protestants do (forensic justification). Justification to a Roman Catholic was like justification+sanctification combined to a protestant. So the Trent condemnation of faith alone for justification is "a classic case of theological misunderstanding, resting upon the disputed meaning of a major theological term" (161). If Trent was read through a Catholic perspective it would read that they are condemning the belief that the entire Christian life can be lived out by faith apart from works (which of course, Protestants do not teach or agree with. You must work to be sanctified, though still by grace). It was also interesting that at another council after Trent (regrettably, I forget the name) Protestants and Catholics almost worked out the misunderstanding.
3) The section on the original reformation was important for me. McGrath showed that there was not one reformation but four (mainly due to geography): The Swiss Reformation (Reformed), the German reformation (Lutheran), the English reformation (Anglican), and then the radical reformation (Anabaptist, which was based on theology rather than geography). The time I spent thinking through these original reformations was also very influential in me becoming an Anglican. From my perspective, there was no need to consider denominations like Methodism, Pentecostalism, Presbyterianism etc. as they were splits off of the original reformation that I didn't view as necessary. I spent a lot of time thinking about these original reformations by looking at their confessions of faith and what made them distinct. I loved the minimalism of the 39 Articles of Faith and that it best understood what the essentials really are: the three ecumenical creeds.
If you're looking to grow in your understanding of church history and how theology developed, I highly recommend this book.