Helmut Koester
Introduction to the New Testament:
Volume one: History, Culture, and Religion of the Hellenistic Age
Fortress Press, 1982.

This, the first of a two volume set, focuses particularly on the Greek or Hellenistic context that shaped the formation of the New Testament. This is Prof. Koester's specialty, and this reflects the work of a career. Why the importance of this perspective? For one thing, the NT is written in Greek, not Hebrew. Early Christian theology is shaped by this context as well.