He was not that Light: John the Baptist was a light, as all saints are light in the Lord, Ephesians 5:8; nay, in a peculiar sense our Saviour beareth him witness, that he was a burning and shining light; but he was not that Light before mentioned, 1 Thessalonians 1:5, that shineth in darkness; and again 1 Thessalonians 1:9 which lighteth every man that cometh into the world. John borrowed his light from that original Light; that Light was God, he was but a man sent from God. The men of the world are ordinarily in extremes, either wholly rejecting God's ministers and witnesses, or else adoring them; as the world is concerned to take heed of the former, so the ministers of Christ are also highly concerned not to admit the latter. See Luke 7:33 Acts 14:13,14; but both John here, and Paul there, were very cautious not to rob their Master of the honour due unto him alone. But was sent to bear witness of that Light: John, as was said before, came only to bear witness of that Light, that he was come, and shined forth, and was the true Light, as it followeth.
Related Commentaries of John 1:8
John 1:8
8 He was not that Light, but was sent to bear witness of that Light.