One of the reasons the jews rejected Jesus was they believe Elijah has to come before the messiah comes. They didn't know Elijah did come. In Jesus's own words:
Matt 17
10 And his disciples asked him, saying, Why then say the scribes that Elias must first come?
11 And Jesus answered and said unto them, Elias truly shall first come, and restore all things.
12 But I say unto you, That Elias is come already, and they knew him not, but have done unto him whatsoever they listed. Likewise shall also the Son of man suffer of them.
13 Then the disciples understood that he spake unto them of John the Baptist.
Malachi 4:5 Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD:
Luke 1
13 But the angel said unto him, Fear not, Zacharias: for thy prayer is heard; and thy wife Elisabeth shall bear thee a son, and thou shalt call his name John.
...
17 And he shall go before him in the spirit and power of Elias, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just; to make ready a people prepared for the Lord.
John the Baptist was the prophet that did come in the power and spirit of Elijah before the coming of the LORD.
Interestingly the jews are still waiting for Elijah to reincarnate on the first day of the week of Unleaven bread. John the Baptist was born on that day.
Jesus honored John as the greatest ever among men.
"The prophet John was the connecting link between the two dispensations. As God's representative he stood forth to show the relation of the law and the prophets to the Christian dispensation. He was the lesser light, which was to be followed by a greater. The mind of John was illuminated by the Holy Spirit, that he might shed light upon his people; but no other light ever has shone or ever will shine so clearly upon fallen man as that which emanated from the teaching and example of Jesus. Christ and His mission had been but dimly understood as typified in the shadowy sacrifices. Even John had not fully comprehended the future, immortal life through the Saviour.
Aside from the joy that John found in his mission, his life had been one of sorrow. His voice had been seldom heard except in the wilderness. His was a lonely lot. And he was not permitted to see the result of his own labors. It was not his privilege to be with Christ and witness the manifestation of divine power attending the greater light. It was not for him to see the blind restored to sight, the sick healed, and the dead raised to life. He did not behold the light that shone through every word of Christ, shedding glory upon the promises of prophecy. The least disciple who saw Christ's mighty works and heard His words was in this sense more highly privileged than John the Baptist, and therefore is said to have been greater than he." -- Desire of Ages p220
