John 1.15-28

¹⁵ (John testified concerning him. He cried out, saying, “This is the one I spoke about when I said, ‘He who comes after me has surpassed me because he was before me.’”) ¹⁶ Out of his fullness we have all received grace in place of grace already given. ¹⁷ For the law was given through Moses; grace and truth came through Jesus Christ. ¹⁸ No one has ever seen God, but the one and only Son, who is himself God and^[b] is in closest relationship with the Father, has made him known.
¹⁹ Now this was John’s testimony when the Jewish leaders^[c] in Jerusalem sent priests and Levites to ask him who he was. ²⁰ He did not fail to confess, but confessed freely, “I am not the Messiah.”
²¹ They asked him, “Then who are you? Are you Elijah?”
He said, “I am not.”
“Are you the Prophet?”
He answered, “No.”
²² Finally they said, “Who are you? Give us an answer to take back to those who sent us. What do you say about yourself?”
²³ John replied in the words of Isaiah the prophet, “I am the voice of one calling in the wilderness, ‘Make straight the way for the Lord.’”^[d]
24 Now the Pharisees who had been sent ²⁵ questioned him, “Why then do you baptize if you are not the Messiah, nor Elijah, nor the Prophet?”
²⁶ “I baptize with^[e] water,” John replied, “but among you stands one you do not know. ²⁷ He is the one who comes after me, the straps of whose sandals I am not worthy to untie.”
²⁸ This all happened at Bethany on the other side of the Jordan, where John was baptizing. John 1 NIV

John 1.15-18 continues to reiterate the information that the last two posts have covered, that those who read or hear this cannot make any mistake as to what the writer means: Christ is God, full exclamation point. "stressing that the Messiah in the closest relationship with God the Father whom no one has ever seen (John 1:18a). Yet the multitudes that saw Yeshua saw ADONAI." further, we should consider the "verb [']has made Him known['], is translated recognized in Luke 24:35, where the two on the road to Emmaus recognized Yeshua when He broke bread with them. It means that Jesus has revealed God the Father to us in such a way that all can recognize Him." Mack Memra of God
 
The next section deals with the actions that the Jewish leaders would take in the event that anyone appeared who might be the Messiah. First, they watched and listened. They have already done so by this point. Then, they sent a delegation to question to person. Finally they made a decision, and either supported the person or reined them in to cease and desist if it was not the Christ (and the person was making statements of being the Christ). Vear p 99 , Mack Messiah Miracles
Vear points out that three times the men from the leaders ask for an answer as to who John the Baptist is, and that they are an official group sent from the Jewish leaders. (99) Vipers John denies being the Christ, and denies being Elijah, though he shares similarities with the prophet, and then denies being The Prophet.
John obviously (to us) was not the Christ, since, obviously (to us) Jesus is. However, the priests had to follow the rules of engagement, and this "John" had been stirring up the people--all the way up to Herod the king.In fact, the people were so stirred up that "Josephus mentioned that the number of people flocking to John were so numerous that Antipas, the ruler of Perea, worried that there might be a popular uprising"Mack  
  GotQuestions** follows through with the confusing part of John being Elijah but not being Elijah. 
If you will recall, Elijah was one of the two men taken from earth to be with God without having died first, the other being Enoch:
 
¹ As they were walking along and talking together, suddenly a chariot of fire and horses of fire appeared and separated the two of them, and Elijah went up to heaven in a whirlwind. 2 Kings 2

  5By faith Enoch was taken from this life, so that he did not experience death: “He could not be found, because God had taken him away.”^a For before he was taken, he was commended as one who pleased God. Heb 11

Logically, then, John the Baptist was not Elijah, but only like him. He did do much that Elijah had done: he was strong with God, he called an entire nation to repentance, and speaking against the king. He had prepared himself in the desert, had dressed and eaten as Elijah. It is also point worthy that Elijah, Moses and Jesus were altogether at the Transifguration---and the men who saw them had seen John the Baptist. GotQuestions, GotQuestions .John the Baptist
As to John's not being the Prophet, he very obviously is a prophet--more than that: "He was a priest by birth because he was the son of Zechariah, but he was called by ADONAI to be a prophet and a preacher" Mack However, the idea of The Prophet is more the idea of the direct mediator between God and man, such as what Moses provided. Of course, John could not be Moses, either, since he was seen at the Transfiguration as well, and this was to be another name for the Messiah. origens commentary

Yet Christ Himself said that John was the greatest of those born, since he was given the duty of clearing and readying the land to hear the voice of God ringing true throughout the byways.  
 

28I tell you, among those born of women there is no one greater than John; yet the one who is least in the kingdom of God is greater than he.” Luke 7

 

John's answers to the questions were preparing the priests for the true Messiah--complete with quoting Isaiah's prophecy to them. Intriguing to me is the fact that he said there is one among you that you do not know. After studying the opening statements as I have, I have changed what I always thought that section meant. I had always thought it just meant that they did not know who Jesus was...and while that might also be the case, I think it means that they did not know who Jesus was. They would not understand and recognize, not all of them, nor the people listening, who He really was. They would not see Him as God because they did not know God---they would not or could not recognize Him as who He was.