Helmut Koester, one of today's foremost New Testament scholars, offers a lifetime's insights into the message of the historical Jesus and the traditions, practices, and trajectories that shaped the Gospels and other early Christian literature including "Q" and the Gnostic Gospels.
This is cutting edge New Testament research very finely digested by the late Helmut Koester in 2007. For a serious Christian with the proper background in New Testament research since WWII, one can read this and get a wonderful overview on how the Apostolic generation and the next two-three generations developed the New Testament. As Scott Hahn clearly states in his book, Letter and Spirit, the writings were developed within the community's liturgies. This is just some rather detailed explanations and includes several other sources from Q, Gospel of Thomas, Dialogue of the Savior, the Didache, as well as the Gospels & Epistles. It is fascinating what we can understand today from these source materials. I do not recommend this book for anyone but scholars with a background in the field. A person without the proper training could easily be hurt in their faith journey instead of realizing how it brings alive the apostolic generation and how they grappled with what Jesus taught, shared and brought meaning to his resurrection.