I Am Christian

Why does the New Testament refer back to the Old testament saying something like "as foretold by the prophet _____"
And then you go look at the passage it cites and has absolutely nothing to do with the so-called fulfilled prophecy?

eg> In Matthew when it explains that joseph took his family to egypt to hide from harod and says that this fulfills what was said in the OT about god's son coming out of egypt. But when you go back and read it, it's just about a guy and his prostitute wife and how that was a parallel for isreal's relationship with god