This was the consistent message of the prophets, the chief subject of all prophecy. Going right back to the beginning of prophecy, to the beginning of the world, God has been speaking to the human race about the coming Deliverer of mankind.
The entire Bible is prophecy, though it comes in many different forms. Among the myriads of voices that are heard in this world, God’s word needs to be picked out, and treated as incomparably greater and more vital to be heard. Thank God that he has not scattered his word throughout the world and mixed it with worthless human messages. He has kept it separate and distinct, and preserved it as the only message given to the human race.