This is the best book for understanding the concepts of the doctrine of the Trinity you will ever read. And it’s short and comprehensible. The author invokes Krusty the Klown and Borat in some of his explanations, so you know it’s not going to be so high-brow and scholarly that you won’t understand what he is talking about. But Bullivant doesn’t skimp on explaining the Greek concepts of homoousios and hypostasis which are central to the vocabulary of the Trinity. If you want to speak confidently about the Trinity, read this book.