Why was the New Testament written in the Greek language?
Greek was the language of the educated classes in the early days of the Christian church. It was used for commerce and international trade, much as English is today. So the New Testament writers, who were educated folks like St. Paul and Luke, naturally chose Greek. Actually, the more precise name for the language is koine, a popular form of Greek spoken in the biblical regions from the fourth century B.C. and it was used for the 27 books of the New Testament.