>> “Exactly which Old Testament prophecies has Jesus demonstrably already completely fulfilled?” <<
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This has already been explained to you.
He fulfilled the three Spring Feasts, Passover, First Fruits, and Pentecost.
Of these Passover is the primary fulfillment, since it was the sacrifice of his own sinless life to pay our debt of sin. He was our own personal Passover lamb for all time.
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No, no, this has not been EXPLAINED. You merely stated this and told me to go read the Bible. I am asking you to tell me in simple language WHAT are these three prophecies and where in the Old Testament does one find them. If you cannot put it in simple words, at least have the grace to do what others have done and tell me where in the Old Testament to find them. If you know, that is.