I personally think it was his short sermon recorded in John 1 that skyrocketed him past all the rest:
29 The next day John saw Jesus coming toward him, and said, “Behold! The Lamb of God who takes away the sin of the world! 30 This is He of whom I said, ‘After me comes a Man who is preferred before me, for He was before me.’ 31 I did not know Him; but that He should be revealed to Israel, therefore I came baptizing with water.” 32 And John bore witness, saying, “I saw the Spirit descending from heaven like a dove, and He remained upon Him. 33 I did not know Him, but He who sent me to baptize with water said to me, ‘Upon whom you see the Spirit descending, and remaining on Him, this is He who baptizes with the Holy Spirit.’ 34 And I have seen and testified that this is the Son of God.” John 1:29-36
But let me call your attention to John 3:30 he is saying, “He must increase, but I must decrease.”

Did John know that he was headed toward death, or did he simply realize that his place in the grand scheme of things he was a lot less than the Lamb of God. I suggest the ladder, John knew, that his job as preacher was not nearly as important as the one he was sent to preach about.

In this day of the mega church with the mega congregation, it is my prayer that we are not producing mega preachers. And that we all would realize that it is he who is least in the kingdom of heaven that is greater than even John the Baptist.