Greek, the lingua franca of the Roman Empire (ironically, Latin was the language least used in the lands occupied by Rome), enough perhaps to negotiate contracts and deal with customers, but certainly not enough to preach. The only Jews who could communicate comfortably in Greek were the Hellenized Herodian elite, the priestly aristocracy in Judea, and the more educated Diaspora Jews, not the peasants and day laborers of Galilee.