The Learner
Well-Known Member
The term "Son of Man" is one of Jesus' favorite names for Himself. He will refer to Himself using this title several times in the Gospels. This is a phrase which all Jewish people would have recognized (Daniel 7:13). It connects Jesus to Old Testament prophecy. In John 1:51, Jesus used this term while describing angels ascending and descending. Here, He is saying that no person has ever gone to heaven and returned. The only person present on earth who was once in heaven is Christ Himself. In verses 11 and 12, Jesus explains that a person who won't believe earthly claims won't believe heavenly ones, either. If Nicodemus, or anyone else, rejects what Jesus says about heaven, there isn't any other source to which they can go. This is one of the places in John chapter 3 where Jesus makes a claim to "exclusivity." This, in short, means that Jesus is the one and only way to God—there are no other options.

What does John 3:13 mean? | BibleRef.com
No one has ascended into heaven, except He who descended from heaven: the Son of Man. - What is the meaning of John 3:13?
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