The Prohet and the Messiah in John 1:20-21 Why did the Jews in John 1:20-21 ask John the Baptist if he was the Christ and then if he was the Prophet?

Since the coming Prophet mentioned in Deut. 18:18 is the Messiah, it seems that their question was redundant. Or did they just not know that the Prophet and the Messiah were one in the same? I think I may just have answered my own question, but please elaborate.
It’s worth noting that the Jewish religious leaders did not ask John the Baptist outright if he was the Messiah.  They simply asked “Who are you?”  It was John the Baptist who immediately came to the point and said “I am not the Messiah.”  Messiah comes from the Hebrew word ‘mashiach’ and means “anointed one” or “chosen one.”  The Greek equivalent is the word ‘Christos’ or, in English, Christ. The name “Jesus Christ” is the same as “Jesus the Messiah.”

Scripture foretells of TWO prophets to come.  The first would be like Moses (Deuteronomy 18:15, 18).  The Jews expected the Messiah (Christ) to bring spiritual leadership and political redemption to Israel – a prophet like Moses.  But there was another prophecy to do with the coming Messiah, the prophecy about Elijah.  Elijah did not die but was taken up into heaven: 


  “And as they still went on and talked, behold, chariots of fire and horses of fire separated the two of them. And Elijah went up by a whirlwind into heaven” (2 Kings 2:11).


Why did the delegation from the Sanhedrin ask if John the Baptist was Elijah? 


  “Behold, I send my messenger, and he will prepare the way before me. And the Lord whom you seek will suddenly come to his temple; and the messenger of the covenant in whom you delight, behold, he is coming, says the Lord of hosts” (Malachi 3:1).
  
  “See, I will send you the prophet Elijah before that great and dreadful day of the Lord comes” (Malachi 4:5).


The Jews believed that Elijah would return and come back to earth to announce the end time.  They also expected that the prophet like Moses would be associated with the coming of the Messiah.  That is why John was asked if he was Elijah or if he was the Prophet like Moses.  Both prophets would precede the coming of the long-awaited Messiah.

John the Baptist identified himself as the messenger of Isaiah 40:3: “A voice cries: “In the wilderness prepare the way of the Lord; make straight in the desert a highway for our God.”  John the Baptist specifically denied that he was Elijah or that he was the Prophet like Moses or that he was the Messiah (John 1:19-21).  To this day, Jewish Seders include an empty chair at the table in anticipation that Elijah will return to herald the Messiah in fulfillment of Malachi’s word.

The Pharisees who had been sent to question John the Baptist were then forced to acknowledge that John was not the Messiah, he was not Elijah and he was not the Prophet (John 1:25).  The Messiah was identified in Scripture as “the anointed one” – not just a priest, or a prophet, or a king. 


  A Samaritan woman said to Jesus, “I know that Messiah is coming (he who is called Christ). When he comes, he will tell us all things.” Jesus said to her, “I who speak to you am he” (John 4:25-26).  She also acknowledged that Jesus was a prophet (John 4:19).
  
  Jesus asked his disciples, “Who do people say that I am?” And they told him, “John the Baptist; and others say, Elijah; and others, one of the prophets.” And he asked them, “But who do you say that I am?” Peter answered him, “You are the Christ.” And he strictly charged them to tell no one about him” (Mark 8:27-30). As we know, the Greek equivalent of the Hebrew word Messiah is, in English, Christ.


In conclusion, the Jews understood that the prophet like Moses and the prophet Elijah were to be the forerunners of the Messiah, God’s Anointed One.

Sources: New Living Translation and New International Version Study Bible notes.  Additional material: https://www.gotquestions.org/promised-messenger-Malachi.html