John Gill Commentary John 1:15

"John beareth witness of him, and crieth, saying, This was he of whom I said, He that cometh after me is become before me: for he was before me." — John 1:15 (ASV)

John bore witness of him
Which was his office and business, for which purpose he was sent, (John 1:6–8)

and cried ;
this agrees with his work and office, according to the prophecy of him in (Isaiah 40:3) and with the time of his ministry, the year of jubilee; and with the nature of his ministry, which was clear, open, and public; and performed with vigour, and in a powerful manner, with much assurance and certainty, with boldness and intrepidity, and with great zeal and fervency, and in an evangelical way; for it was such a cry as debased the creature, and exalted Christ:

this was he, of whom I spoke ;
when he first entered upon his ministry and baptism, before he saw Christ, or baptized him; see (Matthew 3:11) .

he that comes after me ;
for Christ came into the world after John; he was born six months after him; he came after him to be baptized by him, and attended on his ministry; and came later into the public ministry than he did;

is preferred before me ;
by God, the Father, in setting him up as Mediator; constituting him the head of the church; causing a fulness of grace to dwell in him; appointing him the Saviour of his people; and ordaining him judge of quick and dead. And by the prophets, who spoke much of him, and sparingly of John; and of him as the Messiah and Saviour, and of John only as his harbinger:

And by John himself, who represents him as coming from above, and as above all; and himself as of the earth, earthly: and by all Gospel ministers, and every true believer; and good reason there is for it:

for he was before me ;
which cannot be meant of honour and dignity; for this is expressed before; and it would be proving one thing by the same: nor of his birth, as man; for John in that sense was before him, being born before him; besides, being born before another, is no proof of superior worth; others were born before John, whom he yet excelled:

but of his eternal existence, as the word, and Son of God, who was before John, or any of the prophets; before Abraham, and Noah, and Adam, or any creature whatever: the Arabic and Persic versions read, "for he was more ancient than me"; being from everlasting, from the beginning, or ever the earth was.