The New John Gill Exposition of the Entire BibleJohn 1:30
This is he, of whom it is said…
Either the day before,
as in (John 1:27) , or some time before that, (John 1:15) , when he first
began to baptize, even before Christ came to be baptized by him, and
before he personally knew him; see (Matthew 3:11,13) .
After me cometh a man;
not a mere man, but the man God's fellow: and
this is said, not because he was now a grown man, or to show the
truth of his human nature; but seems to be a common Hebraism, and is
all one as if it had been said, "after me cometh one", or a certain
person: for the sense of this phrase, and what follows,
(See Gill on 1:15).