What new information is being told by John? Was it not always so? Even in the Old Testament? To believe? Jesus said just before the passage you posted:
10 Jesus answered and said unto him, Art thou a master of Israel, and knowest not these things?
Are you denying the mystery which was given to Paul, by Jesus Christ? To preach it unto the gentile first?
Notice: Paul says “mystery”, “my gospel”, “hidden until NOW”, “that ALL nations be saved by grace ALONE”
Romans 16:25-27 King James Version (KJV)
25 Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began,
26 But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
But NOW is made manifest to all nations......John was speaking present tense within Christ’s earthly ministry as you can see, Jesus is with him teaching it....Paul, is with the gentiles “after” Christ ascended......you see???? And received a message “after”......why would Paul need “new” information, being given the mystery, if the message was the same, and the gospel already existed? It say, mystery, hidden until NOW