The New Testament was written in Greek for several reasons.
First, Greek was the common language of the Eastern Mediterranean during the time of Jesus and the early Christian community. The expansion of Alexander the Great's empire in the 4th century BCE had spread the Greek language and culture throughout the region, and it remained the dominant language for several centuries.
Second, Greek was a highly developed language with a rich literary tradition, making it a suitable language for expressing complex theological concepts. The authors of the New Testament were likely influenced by the Hellenistic culture of the time, which placed a high value on philosophy and intellectual discourse.
Third, the use of Greek allowed the authors of the New Testament to reach a wider audience. Greek was a language of commerce and trade, and was widely spoken throughout the Roman Empire. By writing in Greek, the authors of the New Testament were able to communicate with a broad range of people, including Jews and Gentiles, who spoke different languages.
Finally, the use of Greek allowed the early Christian community to establish a common language and identity. As the message of Christianity spread throughout the Eastern Mediterranean, the use of Greek helped to unify the diverse communities of believers and establish a shared understanding of the teachings of Jesus.
In summary, the use of Greek as the language of the New Testament was a practical choice that allowed the authors to communicate effectively with a wide audience, express complex theological concepts, and establish a common language and identity for the early Christian community.