The bond which held the Hellenistic world together despite the fragmentation which began with the death of Alexander and continued thereafter, was Attic koine. Its sphere of influence went far beyond that of Aramaic, the official language of the Persian kingdom. Greek merchants dealt in it, whether in Bactria on the border of India or in Massilia; laws were promulgated in it and treaties concluded in accordance with a uniform basic scheme; it was the language of both diplomats and men of letters; and anyone who sought social respect or even the reputation of being an educated man had to have an impeccable command of it….Impeccable command of the Greek was the most important qualification for taking over Greek culture. The final establishment of and dissemination of the koine was probably the most valuable and the most permanent fruit of Alexander’s expedition.
Martin Hengel. Judaism and Hellenism, pg. 58.