John 3:12-13

V. 12. If I have told you earthly things, and ye believe not, how shall ye believe if I tell you of heavenly things? V. 13. And no man hath ascended up to heaven but He that came down from heaven, even the Son of Man which is in heaven.

And Jesus knows in advance that His word will not be accepted, His witness will not be believed. Not only Nicodemus, but all men that are like him in their position toward divine revelation are so blinded by their reason that they cannot understand. Of things pertaining to this life challenging their attention Jesus had spoken, of regeneration and sanctification; and not even those did they credit, much less have faith in His words. But if they could not understand the easier, the more tangible, that which ought to engage their attention at once, what would be the result if Christ should begin to teach of matters not open to human observation and experience, things wholly in the unseen, the essence and purposes of God?

Of those things He could speak and testify of His own personal experience. No human being has ever dwelt in heaven and thus gained a knowledge of heavenly things. One only has dwelt there and is able to communicate the true knowledge concerning God and all divine matters. The Son of Man, the God-man, in His great work of atonement, has come down from heaven to be a witness of heavenly things.

And for this He is fully qualified, for He is still in heaven; He is in the closest, the most intimate connection with the two other persons of the Godhead, even though His body is walking the earth in weakness and humility. Christ here states expressly that He was in heaven from the beginning, for else He could not have come down; that He has now come down for the purpose of testifying of heavenly things; that He is still in heaven, also according to His human nature, as the Son of Man. Compare chap. 1, 18. And finally, the time is coming when He will return to heaven, when His human nature will be finally and fully translated into the heavenly glory and majesty.

"Flesh and blood cannot get to heaven; only He ascends up to heaven that came down from heaven, in order that the government over all may be in His hand. Whatever lives He can kill; and what is dead He can make alive; what is rich He can make poor. Thus it is here resolved, whatsoever is born of flesh does not belong into heaven. But this ascending into heaven and the coming down was done for our benefit, in order that we, who are carnal, might also get to heaven, but with this form, that the mortal body first be killed" (Luther, 11, 1160).