Have you ever wondered why Moses and Elijah were with Jesus on the Mount of Transfiguration? Why wasn’t David, Abraham, or someone else?
The Law and the Prophets
If there was anyone in the Bible that we associate with the Law of God, it is Moses. Moses and the Law are mentioned frequently together in the Old Testament and the New Testament. Even during Jesus’ earthly ministry, Moses and the Law were usually connected. The Apostle John wrote “the law was given through Moses; grace and truth came through Jesus Christ” (John 1:17). The Lord says, He “spoke to you while I was still with you, that everything written about me in the Law of Moses and the Prophets and the Psalms must be fulfilled” (Luke 24:44, and they were. In reality, the Law and the Prophets all pointed to Jesus. Philip told Nathaniel, “We have found him of whom Moses in the Law and also the prophets wrote, Jesus of Nazareth, the son of Joseph” (John 1:45). Jesus was actually prophesied to come as far back as Genesis 3:15, right after the Fall, but also in Deuteronomy 18 where Moses wrote, “The Lord your God will raise up for you a prophet like me from among you, from your brothers—it is to him you shall listen” (Duet 18:15), so God “will raise up for them a prophet like you from among their brothers. And I will put my words in his mouth, and he shall speak to them all that I command him. And whoever will not listen to my words that he shall speak in my name, I myself will require it of him” (Deut 18:18-19). Of course, many did listen to Him (Jesus Christ), but many others didn’t (John 6:66). God will require it of all who reject Christ someday (Rev 20:12-15).
There is no doubt that Moses is associated with the Law, even though it is actually the Law of God. Moses didn’t come down off the Mountain with his own law, but God’s. Maybe it was because he was so involved in recording the Old Testament laws that they thought of those laws as his, or it could be that since Moses personally received the Law from God Himself, they connected him with God’s Law. Either way, the best summary of the Law and the Prophets comes from Jesus. In an unsuccessful attempt to test or trap Jesus, “a lawyer, asked him a question to test him. “Teacher, which is the great commandment in the Law” (Matt 22:35-36)? Jesus said, “You shall love the Lord your God with all your heart and with all your soul and with all your mind. This is the great and first commandment” (Matt 22:37-38), so our first devotion is to God, but then Jesus said that “a second is like it: You shall love your neighbor as yourself” (Matt 22: 39). We must love God first and then love our fellow man. It is on “these two commandments depend all the Law and the Prophets” (Matt 22:40). The laws of God point to loving God and loving man, just as the prophecies point to Jesus Christ.
If you’ve ever read the end of Isaiah 52 and all of Isaiah 53, you surely understand that this is written about the Lord, Jesus Christ…the suffering servant. Isaiah and the other prophets all wrote about Jesus, but even the Law pointed to the work of Christ on the cross in the sacrificial system. Who else could it be but Jesus where it is said that “the Lord has laid on him the iniquity of us all” (Isaiah 53:6b)? It was not a prophet or a king who he wrote about, but of Christ. Isaiah wrote that the intention was to make “his soul…an offering for guilt” (Isaiah 53:10b). There are hundreds of prophecies of Jesus Christ, often mentioning the Messiah or “My Righteous One” by name. King David foretold what Jesus’ excruciating words on the cross would be, writing, “My God, my God, why have you forsaken me” (Psalm 22:1)? And this was a thousand years before Jesus was born into flesh (John 1). Other prophecies about Jesus include Psalm 16, 21, 23, 118, Jeremiah 31:31, Isaiah 61 and dozens more. That’s why Elijah appeared on the Mount of Transfiguration with Jesus. He represented all the prophets who wrote about Him. And of course, Moses was there because he represented the Law of God, but Jesus took the Law and kept it perfectly, as the Prophets foretold, and brought the grace of God, which is apart from the Law.
The whole summary of the Law and the Prophets was given by Jesus Himself. He said we are to love God above all and then love our neighbor as ourselves, and from the Parable of the Good Samaritan, we know that our neighbor is anyone in need, so why did Jesus bring Elijah and Moses to the Mount of Transfiguration? Because Jesus perfectly fulfilled the prophecies of old and He kept the Law after no man had ever done before. Jesus may have also wanted Peter, John, and James to know that the kingdom of God would not consist of temporary booths or Jesus taking over political power (Matt 17:4), but rather, He would come to rule the world in righteousness as King of kings and Lord of lords. Jesus also wanted them to know that John the Baptist’s ministry was the fulfillment of the scribes saying “that first Elijah must come” (Matt 17:10). Jesus clearly told them that “that Elijah has already come, and they did not recognize him, but did to him whatever they pleased. So also the Son of Man will certainly suffer at their hands” (Matt 17:12). He was referring to John the Baptist who was beheaded, and similarly, Jesus said that “the Son of Man will certainly suffer at” the same hands that took John’s life.
I find it interesting that Peter, John, and James already knew who Moses and Elijah were. They seemed to know them without even being introduced or having seen them before, but I’m not sure why they knew them already. And, it would have been interesting to hear what Jesus, Moses, and Elijah were talking about on the Mount of Transfiguration. There’s no indication that the disciples heard any of it, but they did get a glimpse of the glory of the Son of God, and the glorified states of those who die in the faith. I remember Jesus saying that even if a person dies, and they believe in Him, they shall live again (John 11:25-26). More than once, Jesus reminded them that God is the God of the living and not the dead (Matt 22:32; Mark 12:27; Luke 20:38), so even though Moses and Elijah died thousands of years ago, they are still living and in the presence of the Lord. Whoever has trusted in Christ will live again, or if they are living, be joined with the Lord at His return. Then we can ask Jesus, Moses, and Elijah what they were talking about.
Here is some related reading for you: What Was the Transfiguration About? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.