I see you say that one reason Christianity is the true religion is because of the prophecies. But you quote most propheciess from the the Old Testament! Wouldn’t this gives more validity to Judiasm rather than Christianity? If the response is that Jesus fulfilled the prophecies written about in the Old Testament- how do I know that is true except for the fact that it says it in the New Testament. (it’s kind of like a circlar argument).
I would say that if, indeed these messianic prophecies were all fulfilled in spectacular fashion by Jesus, that would lend credence to the inspiration of the Old Testament. Yes, this would give credence to Judaism. However, if Jesus did in fact fulfill the messianic prophecies, that would mean that he is what he said he is, which is the Messiah who was promised in the Old Testament. In that case, true Jews would listen to their Messiah, and, obviously become a Christian. In fact, even today many Jews do become Christians. It is possible to be Jewish and Christian at the same time, although Jewish Christians are not required to keep all the requirements of the Law of Moses, some do so anyway out of a desire to honor their heritage.
As for the fulfilling of the prophecies–whether we are forced to rely on the New Testament testimony for its fulfillment, the answer is that for some we have only the testimony of the New Testament authors and for others we do not. As examples of prophecies which Jesus certainly did fulfill, and which we have outside authorities confirming this, a few can be mentioned. For example, in Psalm 22:16 it says of the Messiah, "they have pierced my hands and my feet." We know both from the Babylonian Talmud and from Tacitus, a Roman historian, that Jesus was crucified. There is a prophecy in Micah 5:2 that the Messiah would be born in Bethlehem and in Isaiah 9:1 that the Messiah would come from Galilee, in "the land of Zebulun and Naphtali." Both of these facts about Jesus are know from sources outside of scripture. Then there is the fact that he was "despised and rejected by men" in Isaiah 53:3, which is clearly known from other sources, including Josephus. Another example is Daniel 9:24-25 which predicts that the Messiah would come to Jerusalem to make atonement for sin somewhere between AD 26-33. We know that this timing is correct from outside sources as well. So, it is true that many of the prophecy fulfillment is testified only from New Testament writers, but in the case of several, we have outside confirmation.
Even for those which are confirmed by NT writers (betrayed for 30 pieces of silver, money used to buy the potter’s field: Zechariah 11:12-14 and many others), this is not circular reasoning. It is the simple reporting of a fact by a reliable witness. There is no evidence that Matthew, John and the other gospel writers were liars. In fact, they reported details such as the 30 pieces of silver when many of the eye-witnesses to the event, presumably many of them not followers of Jesus, were still alive. There is no reason to believe that the gospel writers were liars. Either way, this is not circular reasoning. Circular reasoning is when one tries to prove something by assuming it is true before asking the question. The fact that some of the historical record of the fulfillment of OT prophecies is found in the New Testament is not, by definition, circular reasoning.