John 3:13

13.No one hath ascended to heaven. He again exhorts Nicodemus not to trust to himself and his own sagacity, because no mortal man can, by his own unaided powers, enter into heaven, but only he who goes thither under the guidance of the Son of God. For to ascend to heaven means here, “to have a pure knowledge of the mysteries of God, and the light of spiritual understanding.” For Christ gives here the same instruction which is given by Paul, when he declares that

the sensual man does not comprehend the things which are of God,
(1 Corinthians 2:16;)

and, therefore, he excludes from divine things all the acuteness of the human understanding, for it is far below God.

But we must attend to the words, that Christ alone, who is heavenly, ascends to heaven, but that the entrance is closed against all others. For, in the former clause, he humbles us, when he excludes the whole world from heaven. Paul enjoins

those who are desirous to be wise with God to be fools with themselves,
(1 Corinthians 3:18.)

There is nothing which we do with greater reluctance. For this purpose we ought to remember, that all our senses fail and give way when we come to God; but, after having shut us out from heaven, Christ quickly proposes a remedy, when he adds, that what was denied to all others is granted to the Son of God. And this too is the reason why he calls himself the Son of man, that we may not doubt that we have an entrance into heaven in common with him who clothed himself with our flesh, that he might make us partakers of all blessings. Since, therefore, he is the Father’s only Counselor, (Isaiah 9:6,) he admits us into those secrets which otherwise would have remained in concealment.

Who is in heaven. It may be thought absurd to say that he is in heaven, while he still dwells on the earth. If it be replied, that this is true in regard to his Divine nature, the mode of expression means something else, namely, that while he was man, he was in heaven. It might be said that no mention is here made of any place, but that Christ is only distinguished from others, in regard to his condition, because he is the heir of the kingdom of God, from which the whole human race is banished; but, as it very frequently happens, on account of the unity of the Person of Christ, that what properly belongs to one nature is applied to another, we ought not to seek any other solution. Christ, therefore, who is in heaven, hath clothed himself with our flesh, that, by stretching out his brotherly hand to us, he may raise us to heaven along with him.