Eliyahu HaNavi- Elijah the Prophet; part 1: Elijah's Cup

A good friend of the family's recently had a question about Elijah's role in Judaism, so I thought I would make an overview of it the first blog topic, a series, rather.
This one is geared more for LDS readers, as our friend is LDS, but the information should be of interest to all.

Every Passover, before the passage pour out thy wrath upon the heathen (Psalm 79:6-7) is read, an extra cup- usually the fanciest one- is placed on the table and filled with wine. None of the guests or family touch it, and the door often is opened. This cup is for Elijah the Prophet, who according to legend wanders around the houses of the Jews at Passover time. The origins of this legend are unclear, one theory is that it developed among Jews in Christian lands. In the Middle Ages (and in Eastern Europe until quite recently), Passover was not only a solemn and joyous occasion, but also one of fear and trepidation. This was when blood libels were made against the Jews. A Christian belief was that Jews lured Christian children and murdered them, using their blood to make matzahs (the Passover unleavened bread). This was used to whip the mob into a frenzy of righteous indignation, which resulted in severe violence against the Jews and their property. Among the jews the legend developed that Elijah was sent to protect them from the rioters and so wandered around their homes, much like a policeman patroling his beat. The door was opened to make sure that there were no spies lurking, eavesdropping, or that no dead bodies were placed by their homes.
This legend became intertwined with the tradition of Elijah's cup, which has its origins in an entirely different matter, that of the controversy of the five cups.

The theme of the Passover is salvation and redemption. The Exodus from Egypt is only the backdrop. Despite the repeated allusions tto the past, the focus is on the present and the future.
The Passover haggadah states that in every generation a man must see himself as being led out of Egypt, and must teach this to his sons too. The past is merely a reminder of what the future will be.
One of the Passover scriptures is Exodus 6:6-8:

Wherefore say unto the children of Israel, I am the Lord and I will bring you out from under the burdens of the Egyptians, and I will rid you out of their bondage, and I will redeem you with a stretched out arm, and with great judgments, and I will take you to me for a people, and I will be to you a God: and ye shall know that I am the Lord your God, which bringeth you out from under the burdens of the Egyptians.
And I will bring you unto the land, concerning the which I did swear to give it to Abraham, to Isaac, and to Jacob; and I will give it to you for an heritage: I am the Lord.

At the Passover, four cups are drunk, commemorating the four acts of salvation I marked in bold in that verse. A closer look will show that there are actually five acts. There should be five cups, but as this custom arose in Babylon at a time of exile, several of the Geonim (the spiritual leaders of Babylonian and most world Jewry from the 6th to 11th centuries) several were unsure of the propriety of drinking a cup commemorating being brought into the land, when they were not in it.
Following a sharp controversy, it was decided to settle on a compromise. Five cups could be poured, but only four were to be drunk. The fifth one was set aside for Elijah, meaning that when he would come again as the messenger of the covenant, to herald the Messiah, he would settle all disputes of Jewish law.