John 1:7-8

This man came as a witness in order to testify concerning the Light, that all men through Him might believe. He was not this Light, but was sent in order to testify concerning the Light.
John 1:7-8, Modern English Version (MEV)
 
From Albert Barnes’ Notes on the Bible:
 
For a witness - To give testimony. He came to prepare the minds of the people to receive him Matt. 3; Luke 3; to lead them by repentance to God; and to point out the Messiah to Israel when he came, Jhn_1:31.
 
Of the Light - That is, of the Messiah. Compare Isa_60:1.
 
That all men ... - It was the object of John’s testimony that all people might believe. He designed to prepare them for it; to announce that the Messiah was about to come, to direct the minds of men to him, and thus to prepare them to believe on him when he came. Thus, he baptized them, saying “That they should believe on him who should come after him” Act_19:4, and thus he produced a very general expectation that the Messiah was about to come. The testimony of John was especially valuable on the following accounts:
 
1. It was made when he had no personal acquaintance with Jesus of Nazareth, and of course there could have been no collusion or agreement to deceive them, Jhn_1:31.
 
2. It was sufficiently long before he came to excite general attention, and to fix the mind on it.
 
3. It was that of a man acknowledged by all to be a prophet of God - “for all men held John to be a prophet,” Mat_21:26.
 
4. It was “for the express purpose” of declaring beforehand that he was about to appear.
 
5. It was “disinterested.”
 
He was himself extremely popular. Many were disposed to receive him as the Messiah. It was evidently in his “power” to form a large party, and to be regarded extensively as the Christ. This was the highest honor to which a Jew could aspire; and it shows the value of John’s testimony, that he was willing to lay all his honors at the feet of Jesus, and to acknowledge that he was unworthy to perform for him the office of the humblest servant, Mat_3:11.
 
Through him - Through John, or by means of his testimony.
 
Was not that Light - Was not “the Messiah.” This is an explicit declaration designed to satisfy the disciples of John. The evidence that he was not the Messiah he states in the following verses.
 
From the conduct of John here we may learn,
 
1. The duty of laying all our honors at the feet of Jesus.
 
2. As John came that all might believe, so it is no less true of the ministry of Jesus himself. He came for a similar purpose, and we may all, therefore, trust in him for salvation.
 
3. We should not rely too much on ministers of the gospel. They cannot save us any more than John could; and their office, as his was, is simply to direct people “to the Lamb of God that taketh away the sin of the world.”