>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.
Elijah is the Spirit of Christ, or self sacrifice. Everyone gets tested by the Spirit of Truth, but when it comes, they do whatever that they want with it and thwart bearing their own cross for God's Kingdom come. John is the one who witnessed Christ and baptized him with water (mercy). He made is path straight and clear and preached his coming, was waiting for Him.