Charles Ellicott Commentary John 1:27

"[even] he that cometh after me, the latchet of whose shoe I am not worthy to unloose." — John 1:27 (ASV)

He it is . . . is preferred before me.—These are insertions made to harmonize the verse with John 1:15; John 1:30. If we omit them, "He who comes after me" is the subject of the verb "stands," and the entire sentence is: He who comes after me, the thong of whose sandal I am not worthy to unloose, stands among you and you know Him not.

This reading provides the authority for baptism, the outward sign of the Messiah’s advent, for He is already standing in their midst. Here is the answer to their question. John’s work is simply ministerial. The baptism of the Spirit is at hand. The coming One has come. (Compare Notes on Matthew 3:11 and Mark 1:7.)