Jamieson, Fausset and Brown on John 1:15

Joh 1:15. A Saying of the Baptist Confirmatory of This.

15. after me--in official manifestation.

before me--in rank and dignity.

for he was before me--in existence; "His goings forth being from of old, from everlasting" (Mi 5:2). (Anything lower than this His words cannot mean); that is, "My Successor is my Superior, for He was my Predecessor." This enigmatic play upon the different senses of the words "before" and "after" was doubtless employed by the Baptist to arrest attention, and rivet the thought; and the Evangelist introduces it just to clinch his own statements.