Albert Barnes on John 1:20

I am not the Christ. This confession proves that John was not an impostor. He had a wide reputation. The nation was expecting that the Messiah was about to come, and multitudes were ready to believe that John was he, Lk 3:15. If John had been an impostor he would have taken advantage of this excited state of public feeling, proclaimed himself to be the Messiah, and formed a large party in his favour. The fact that he did not do it is full proof that he did not intend to impose on men, but came only as the forerunner of Christ; and his example shows that all Christians, and especially all Christian ministers, however much they may be honoured and blessed, should be willing to lay all their honours at the feet of Jesus; to keep themselves back and to hold up before the world only the Son of God. To do this is one eminent mark of the true spirit of a minister of the gospel.