He said in reply, "Elijah will indeed come and restore all things; but I tell you that Elijah has already come, and they did not recognize him but did to him whatever they please. So also will the Son of Man suffer at their hands." (NAB) Matthew 17:11-12
Jesus had said to his disciples that John the Baptist was Elijah, and that Elijah had come before them to prophesy about his coming. Not only that he says Elijah will come and restore all things. That would mean that Elijah had come twice for the sake of the Kingdom. The name Elijah means (Heb. 'Eliahu, "Yahveh is God"; also called Elijah). This is from the catholic encyclopedia.
We did not recognize him, because he came to us as one of us. To prepare us for his Son. Since we didn't recognize him then either we treated his Son just as bad. That tells me something very powerful, that God loves us so much to be with us in a human way. For us to realize the depths he would go; to see that we have life in him. Would we go to those lengths for others so they would have life also?