This remarkable event is recorded in Matthew 17, Mark 9, and Luke 9.  It was six days after the Lord began to tell His disciples of His death and resurrection as we read in Matthew 16:21, “From that time forth began Jesus to shew unto his disciples, how that he must go unto Jerusalem, and suffer many things of the elders and chief priests and scribes, and be killed, and be raised again the third day.”  The Lord took three of His disciples (Peter, James, and John) and led them to a high mountain apart from all others.  Luke 9:28 tells us that He took them there to pray.  There, the Lord was transfigured and His appearance changed, so that “…his face did shine as the sun, and his raiment was white as the light.” (Matthew 17:2).  What a sight this must have been for those men to witness this transformation of the Lord.  The Greek word for transfigured is “metamorphóō” which is where we get the word ‘metamorphosis’.

We read in Matthew 17:3, “And, behold, there appeared unto them Moses and Elias talking with him.”  Somehow, the disciples knew the identity of these men for we read in Mark 9:5, “And Peter answered and said to Jesus, Master, it is good for us to be here: and let us make three tabernacles; one for thee, and one for Moses, and one for Elias.”  Why was it that these men appeared there with the Lord?  I think we can readily see these two represented the Law (Moses) and the prophets (Elias, or Elijah), so it was a confirmation from the Old Testament as to the person of the Lord Jesus, the fulfillment of the prophesy of the coming Messiah.  (There is also a wonderful type of the Rapture of the church where some will be taken to Heaven without dying, pictured in Elijah who never died.  Others will be resurrected and taken to Heaven pictured by Moses who had died and was now living in the presence of the Lord.) 

The topic of discussion between the Lord and Moses and Elijah is given to us in Luke 9:31, where we learn they, “spake of his decease which he should accomplish at Jerusalem.”  These Old Testament men were fully aware of the plan of God that the Lord Jesus would die for the sins of ungodly men.  We also have the confirmation of God as to the person of Christ given to us in Luke 9:35, “And there came a voice out of the cloud, saying, This is my beloved Son: hear him.”  There is so much to be learned from this amazing incident, but we should look at your question: What was the purpose of the Mount of Transfiguration?

Let’s go back and read Matthew 16:28 where the Lord told His disciples, “Verily I say unto you, There be some standing here, which shall not taste of death, till they see the Son of man coming in his kingdom.”  This He said in reference to His upcoming transfiguration.  Indeed, as the Lord said, ‘some’ of them would see the Lord coming in His kingdom before dying.  That was Peter, James, and John.  In the transfiguration they were privileged to witness a preview of Christ seen in the glory of His kingdom.  Although the Lord told them men not to mention what they had seen “until the Son of man be risen again from the dead.” (Matthew 17:9), it was after the Lord’s death and resurrection that Peter wrote of this incident in 2 Peter 1:16, “For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were EYEWITNESSES OF HIS MAJESTY.”  Perhaps John was speaking of this incident when he wrote in John 1:14, “And the Word was made flesh, and dwelt among us, (and WE BEHELD HIS GLORY, the glory as of the only begotten of the Father,) full of grace and truth.”

So, we see the purpose of the transfiguration was to confirm Jesus as the Messiah and as the Son of God.  It was demonstrated that He was not merely a human teacher or a miracle worker. His appearance and conversation with Moses and Elijah show His fulfillment of the Law and the prophets. The voice from the cloud declaring Jesus as God’s beloved Son revealed His divine nature and unique relationship with the Father. For us today, the transfiguration challenges believers to acknowledge Jesus’ complete authority in our lives and to respond by listening to Him and following His teachings.  (CC)  (717.4)