The adverb hellenisti means 'in the Greek language' or 'in Greek.' It appears in Acts 21:37 and John 19:20, marking the use of the Greek tongue as a distinct and significant choice.
When Paul, about to be brought into the barracks in Jerusalem, addresses the tribune in Greek (Acts 21:37), the tribune is astonished: 'Do you know Greek?' This moment illuminates Paul's remarkable position as a man who could move between Jewish, Greek, and Roman worlds. His ability to speak hellenisti opened doors to the Gentile world; his Hebrew tongue (Acts 21:40) gained him a hearing from the Jewish crowd. The Gospel itself traveled primarily through the Greek language across the Roman Empire. That the New Testament was written hellenisti was not incidental but providential: God chose the most widely-known language of the Mediterranean world as the vehicle for His final revelation.