John Gill Commentary John 1:30

"This is he of whom I said, After me cometh a man who is become before me: for he was before me." — John 1:30 (ASV)

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 3:11Matthew 3:13) .

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 John 1:15).