Why was Elijah referred to in the New Testament?

Elijah and Elisha together are a type of Christ. Elijah represents Christ before the cross and Elisha after the cross. Elijah's ministry was to call Israel back to the faith of the Fathers Abraham, Isaac and Jacob. He was known for causing it to not rain, and for calling fire from heaven. Elijah represents the law, which we are told is a schoolmaster to bring us to Christ. Elishah represents grace.

John and Jesus together also are a type of Christ. John represents Elijah and preached repentance to call Israel back to the faith of the fathers. He represents the law which can only convict of sin. Jesus represents grace. "This is Elijah" refers to Jesus and John together. In another place the disciples knew that Jesus was speaking of John, refers to John representing the Elijah half of the picture.

Elijah had said there would be no rain until his Word. With water as a symbol of the Word of God, there was no Word from God for four hundred years until John spoke. And in a double fulfillment, Jesus is the Word of God, and he did not begin his ministry until John had spoken.

Furthermore, John's costume was designed to remind people of Elijah.

There is a second context where he is mentioned and that is at the mount of transfiguration. Moses, Elijah and Christ were together. The reason for this is theme wrapped around the number three. The Father, Son and Holy Ghost are revealed through Word, Works and Life. Moses represents the revelation of God through the Word - the Law. Elijah represents the revelation of God through mighty works. And Jesus represents the revelation of God through Life itself, God incarnate. In this theme, we are deaf, blind and lame, but Christ makes us hear, see and walk.

The third context is presumed to be in Revelation as one of the two witnesses. In the same way that Elijah and Elisha, John and Jesus, and Jesus himself represent Law and Grace, so the two witnesses will also represent the two edges of the sWord, or the Word of God.

We know how Jesus represents grace, but how does he also represent the law? His perfect life puts us to shame because he faced the same temptation we do, yet did not sin. By his perfect life he condemns us so that we are without excuse. He is Judge.

So we can approach Christ for mercy or for judgment. Elijah is mentioned in the New Testament to remind us that without the mercy of Christ, we face the judgment of Christ.