"And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven." --- John 3:13.
No mere man whatsoever has entered, or can enter, into the secrets of God's heart in heaven, relating to the great mysteries of salvation, so as immediately and perfectly to understand them, and make them known to others; but the privilege is perculiar to the Messiah, who is spoken of under the character of "the Son of man." Psalm 80:17, and Daniel 7:13, and always had an existence in heaven as the Son of God, and who came from thence into an incarnate state, that he might reveal counsels to men.
As many are perplexed about the Divinity of Christ, the following may help them to conceive of that matter more properly: As the Divine and human natures of Christ were united in the person of Christ, some things are attributed to one nature which properly belonged to the other.
Thus when it is said, 1 Corinthians 2:8, "the Lord of glory was crucified;" and, Acts 20:28, he is called God, "who purchased the church with his own blood;" the meaning is not that he, as the Lord of glory, was crucified; or, as God, shed his blood --- as if the divine nature could be crucified and bleed; but that the person, who was the Lord of glory in one nature, was crucified in the other, etc.
So, when it is said, "The Son of man is in heaven;" the meaning is not, that he, as the Son of man, was there also whilst he was on earth; but that he, who was here in his human nature, was there in his Divine.
My Saviour, whilst he dwelt on earth,
As God in heaven had his abode;
So let me, by an heavenly birth,
Live in the world, yet dwell with God.