So the question iswhat proselytizing religion could spring up in Judea under the Parthian Empire, spreading throughout it as Christianity spread throughout Rome.
- how would Second Temple Judaism without much of an onerous foreign yoke still manage to polarize or alienate a group of Jews into breaking out of the insular world of... Judah and friends, Palestine, whatever
- and, what would the adjacent populations-- take your pick of Arab and other Semitic caravan traders in the inland, coastal Greeks or Hellenophones, Aramaic peoples of western/northern Syria and Iraq, Parthian and Persians in Iraq, and the Egyptians-- actually derive from that?
Were a dispute in Judaism to become acrimonious enough (I guess it would involve disputes over the king's powers) to produce a minor tradition of martyrs/charismatic leaders, I could see the appropriation of this authority being useful for groups similar to those behind the Palmyrene Empire (or more likely a second attempt after an initial failure and suppression), with Aramaic being useful as a language of communication. In fact this is the only thing we can say for sure-- Aramaic would occupy the role of Greek in any such religion