The Spirit of Early Christian Thought (Robert Louis Wilken)
This book is not a polemic or a book of apologetics; it is instead an exposition of what early Church theologians thought about important topics in Christian belief, and how those thoughts evolved and grew. If you think all theology is merely empty wind or arguments about angels dancing on the head of a pin, this is not the book for you. But if you want to know how early Christians developed their thought about the Trinity, or theological views on Christ being simultaneously fully human and fully divine, or how they viewed faith through the prism of reason, this is the book for you.