This book has been over a dozen years in the making:
Gregg R. Allison, Historical Theology: An Introduction to Christian Doctrine; A Companion to Wayne Grudem’s Systematic Theology. Grand Rapids: Zondervan, 2011. 
It’s 778 pages. And that’s the abridged version. Allison writes in the preface, “Even when I turned in the largest rough draft Zondervan had ever received, no one laughed at or chided me. Rather, a calm and simple suggestion was made that I revisit the length of the draft for the sake of keeping the book to one volume.”
The first chapter presents eights ways that historical theology benefits the church (pp. 24–29, numbering added):
- [Historical theology helps the church] distinguish orthodoxy from heresy. . . .
- It provides sound biblical interpretations and theological formulations. . . .
- It presents stellar examples of faith, love, courage, hope, obedience, and mercy. . . .
- [It protects] against the individualism that is rampant today among Christians. . . .
- It not only helps the church understand the historical development of its beliefs, but enables it to express those beliefs in contemporary form. . . .
- It encourages the church to focus on the essentials, that is, to major on those areas that have been emphasized repeatedly throughout the history of the church. . . .
- It gives the church hope by providing assurance that Jesus is fulfilling his promise to his people. . . .
- As beneficiaries of the heritage of doctrinal development sovereignly overseen by Jesus Christ, the church of today is privileged to enjoy a sense of belonging to the church of the past.
