"Remember ye the law of Moses my servant, which I commanded unto him in Horeb for all Israel, with the statutes and judgments.As long as I can remember, it's been pretty clear to me why Elijah is mentioned at the end of Malachi: the appearance of Elijah (and others) to Joseph Smith is pretty central to my religion. But what does Moses and Mount Horeb have to do with that?
"Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse." (Malachi 4:4-6)
"Specially the day that thou stoodest before the LORD thy God in Horeb, when the LORD said unto me, Gather me the people together, and I will make them hear my words, that they may learn to fear me all the days that they shall live upon the earth, and that they may teach their children." (Deuteronomy 4:10)Moses and Horeb are like Joseph and the Grove: the prophet and the place where religion originated. We could view Horeb as the place where the "Old" Testament began, in the sense that it is where the LORD establishes his covenant (in writing) with Israel (Deuteronomy 5:2).
But another prophet also went to Horeb:
"And [Elijah] arose, and did eat and drink, and went in the strength of that meat forty days and forty nights unto Horeb the mount of God.Elijah's experience on Horeb was different from his forebear's: Moses received the Law, establishing a covenant with a nation; Elijah's was a personal manifestation of the LORD, renewing his prophetic calling---or, in a way, his personal covenants.
"And he came thither unto a cave, and lodged there; and, behold, the word of the LORD came to him.... And he said, 'Go forth, and stand upon the mount before the LORD.' And, behold, the LORD passed by, and a great and strong wind rent the mountains, and brake in pieces the rocks before the LORD; but the LORD was not in the wind: and after the wind an earthquake; but the LORD was not in the earthquake: And after the earthquake a fire; but the LORD was not in the fire: and after the fire a still small voice." (1 Kings 19:8-12)
(How fitting that both prophets were translated and would later appear together on another mount.)