The book "Ancient Church: History, Doctrine, Worship and Constitution" by W. D. Killen is a detailed study of the period of development of Christianity in the early era. The author examines in detail the history of religious changes and events that took place in the first centuries of Christianity, outlining the main teachings, worship rituals and the structure of the Church of that time. In this book, you will find comprehensive information about the development of early Christian currents, the emergence of canonical texts, as well as the influence of religious and political events on the formation of the church structure. By reading this book, you will be able to better understand the important events and transformations that took place in the Christian Church during the first golden age of its existence.