He was not that Light, but was sent to bear witness of that Light.
To mistake the forerunner for the Messiah, the Baptist for the Christ, the man for the Lord, was not the first characteristic blunder of the Church against her Divine Head. It repeated Eve's mistake of her firstborn for the firstborn of God. If we had not seen the subsequent errors of the Church, we should have been almost tempted to count John's statement unnecessary, perhaps gratuitous, that the Baptist was "not that Light." The only true relation of any ordinance is that of testimony to Christ. At the point where an ordinance ceases to testify of Christ, there it begins to betray Him. Then the betrayal of a Judas is followed by the denial of a Peter. The agency of priestcraft is at the bottom in either case. A false apostle sells, false priests buy, and Christ is crucified between them. The symbol of the thirty pieces of silver is, the nominal Christian barters to the nominal Jew the Divine reality. And so it has been in all ages and with every heresy. You cannot reconcile priestcraft and Christ-craft: they are the antagonism of God and mammon. The process is in every case essentially the same, confounding the testifier with the thing testified. Men began first to mingle representative rites with spiritual realities, then inseparably to unite them, and lastly to identify forms with the spiritual facts which they symbolized. Hence arose the transubstantiation of one sacrament, and the transpiritualism of the other. Transubstantiation, which identifies the Lord's body with the bread and wine which He appointed as its symbolic testifiers, and transpiritualism, which identifies the baptism of the Spirit with that of water, are cognate heresies. The ordinance, in either case, displacing the Ordainer, the form neutralizing the fact, and compelling us to protest against sacramentalism on behalf of the sacraments, as well as on the part of the Saviour, that sacramental elements are "not that Light, but sent to bear witness of that Light."
(J. B. Owen, M. A.)
Parallel VersesKJV: He was not that Light, but was sent to bear witness of that Light.