John 3:12

If. have told you earthly things, and ye believe not.

He had spoken of the things that belonged to the kingdom of God on earth, of the new birth. If Nicodemus could not understand and believe this, so plain, easily understood and connected with human life, how would he receive testimony concerning the heavenly kingdom, God, and eternal glory? He had said: "We know that thou art. teacher, come from God;" Christ now declares that he is not "a man sent from God" like John, but has come down from heaven, still is of heaven, and therefore, can bear witness of heavenly things.