What is the origin of the additional words to John 3:13?

Question

There is a Q regarding the meaning of this verse. This Q is regarding the authenticity of the 'addition' - and what was intended by it. https://hermeneutics.stackexchange.com/questions/25129/what-is-meant-in-john-313-by-the-son-of-man-whos-in-heaven-yet-he-still-says?r=SearchResults&s=4|46.2592

Most modern translations seem to have the following for John 3:13

No one has ascended into heaven, but He who descended from heaven: the Son of Man

Then the KJ and a few others add, 'who is in heaven' so we get the following longer verse.

No one has ascended to heaven but He who came down from heaven, that is, the Son of Man who is in heaven.

The Alexandrian text omits this addition. Does it have veracity and/or what is the point of the addition?

Answer 1

This is Bruce Metzger's commentary on this text. He was an expert on this subject.

  3:13      ἀνθρώπου {B}

On the one hand, a minority of the Committee preferred the reading ἀνθρώπου ὁ ὤν ἐν τῷ οὐρανῷ, arguing that (1) if the short reading, supported almost exclusively by Egyptian witnesses, were original, there is no discernible motive that would have prompted copyists to add the words ὁ ὢν ἐν τῷ οὐρανῷ, resulting in a most difficult saying (the statement in 1:18, not being parallel, would scarcely have prompted the addition); and (2) the diversity of readings implies that the expression ὁ υἱὸς τοῦ ἀνθρώπου ὁ ὤν ἐν τῷ οὐρανῷ, having been found objectionable or superfluous in the context, was modified either by omitting the participial clause, or by altering it so as to avoid suggesting that the Son of Man was at that moment in heaven. On the other hand, the majority of the Committee, impressed by the quality of the external attestation supporting the shorter reading, regarded the words ὁ ὢν ἐν τῷ οὐρανῷ as an interpretative gloss, reflecting later Christological development. -- Metzger, B. M., United Bible Societies. (1994). A textual commentary on the Greek New Testament, second edition a companion volume to the United Bible Societies’ Greek New Testament (4th rev. ed.) (pp. 174–175). London; New York: United Bible Societies.