One of the reasons that the Gospel spread so rapidly was Pax Romana. And since the Romans had dutifully kicked ass while not taking names, people were forced to learn the conqueror's language.
Paul was a missionary to the non-Jewish types. None of his originals are still around. While he was born into the tribe of Benjamin and came to be a first class Pharisee, it is unlikely that he wrote any of his letters in Hebrew, or Aramaic.
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