Mark 9:2-4

To be absent from the body is to be present with the Lord. Jesus  talked with Moses and Elijah they were present when God spoke to the Apostles.  Jesus brought heaven into the earthly realm of mankind. He is always in control!

Moses was the lawgiver and liberator, while Elijah was the first of the great prophets. Their presence confirmed the reality that Jesus is the Messiah.

Mark 9:2-4

 Now after six days Jesus took Peter, James, and John, and led them up on a high mountain apart by themselves; and He was transfigured before them. ³ His clothes became shining, exceedingly white, like snow, such as no launderer on earth can whiten them. ⁴ And Elijah appeared to them with Moses, and they were talking with Jesus.

²⁸ Now it came to pass, about eight days after these sayings, that He took Peter, John, and James and went up on the mountain to pray. ²⁹ As He prayed, the appearance of His face was altered, and His robe became white and glistening. ³⁰ And behold, two men talked with Him, who were Moses and Elijah, ³¹ who appeared in glory and spoke of His decease which He was about to accomplish at Jerusalem. 

³⁵ And a voice came out of the cloud, saying, ^e“This is My beloved Son. Hear Him!”

Luke 9:28–31 and 35

Now after six days Jesus took Peter, James, and John his brother, led them up on a high mountain by themselves; ² and He was transfigured before them. His face shone like the sun, and His clothes became as white as the light. ³ And behold, Moses and Elijah appeared to them, talking with Him.

 ⁵ While he was still speaking, behold, a bright cloud overshadowed them; and suddenly a voice came out of the cloud, saying, “This is My beloved Son, in whom I am well pleased. Hear Him!” 

Matthew 17:1–3 and 4

⁹ “I watched till thrones were put in place, And the Ancient of Days was seated; His garment was white as snow, And the hair of His head was like pure wool. His throne was a fiery flame, Its wheels a burning fire; 

Daniel 7:9

The NKJ:

9:2 After six days links Jesus’ prediction of v. 1 with the events of vv. 2–8. The high mountain was most likely one of the foothills surrounding Mt. Hermon. They probably did not stand on Mt. Hermon itself, a snowy peak which rises to 9,232 feet. It is the highest point in all of Palestine. These mountains overlook Caesarea Philippi, where Peter’s confession was made (8:27–29). Jesus’ transfiguration deeply affected John and Peter, who mention it in their writings (see John 1:14; 2 Pet. 1:16–18).

9:4 Elijah is mentioned in Mal. 4:5, 6 in connection with the future coming of Christ. This is why people asked John the Baptist if he were Elijah (John 1:21). Moses was the lawgiver and liberator, while Elijah was the first of the great prophets. Their presence confirmed the reality that Jesus is the Messiah of Peter’s confession.