John 6:45, "It is written in the prophets, And they shall be all taught of God. Every man therefore that hath heard, and hath learned of the Father, cometh unto me."
JOHN 6:40-45
The Old Testament prophets prophesied of a new covenant where we would all be taught of God. This is speaking of revelation knowledge that comes from within, through our spirit. Under the Old Covenant, God dealt with the Jews through the outer man. He did this because an Old Covenant man (who was not born again) could not perceive the spiritual truths revealed in the New Covenant by the Spirit (1 Cor. 2:14). This difference between the old and new covenants is the reason why there had to be two covenants.