Something extraordinary happened when Jesus went up to the mountain with three of His disciples. Two men showed up to Jesus on the mountain from heaven. Moses and Elijah. They spoke with Jesus about His exodus from the earth, referring to His death and resurrection. It also reveals and tells us something else. Moses and Elijah have meanings and so does Jesus. All three were revealing the completion of God’s revelation.
Moses and Elijah’s meaning is found in Luke 16. Let’s take a look at it.
29 But Abraham said, ‘They have Moses and the Prophets; let them hear them.’ 30 But he said, ‘No, father Abraham, but if someone goes to them from the dead, they will repent!’ 31 But he said to him, ‘If they do not listen to Moses and the Prophets, they will not be persuaded even if someone rises from the dead.’” -Luke 16:29-30
The rich man that died who was now found to be in hell, asked Abraham to send to his brothers Lazarus, so that they may be convinced through a miracle—a resurrection, to get saved and avoid ending up with him in hell.
How did Abraham answer him? He said to him that his brothers already know how to avoid hell by finding God in the writings of Moses and the prophets. Basically, Moses and the prophets are synonymous for the Scriptures.
Now, getting back to Jesus being in the mountain with Moses and Elijah. These two men represent the old testament. Moses, the Pentateuch which is Genesis through Deuteronomy. Elijah represents the rest of the Old Testament which were writing by the prophets. Jesus represents the New Testament. So, what we see in the Mount of configuration is the completion of the whole revelation of God to men. You see the plan of redemption for mankind in those three men, in the Old and New Testament. The Old Testament pointed to Jesus, the sacrificial Lamb of God to take away the sins of the world. When Jesus came, He fulfilled the prophecies spoken about Him.
There is nothing more to add to God’s Word, it is completed. To avoid hell, one must read the Bible to find Jesus and read what He did for them on the cross and afterward, His resurrection, proving that everything He taught is true.