After six days Jesus took Peter, James, and John his brother, and led them up a high mountain by themselves. And he was transfigured before them; his face shone like the sun and his clothes became white as light. And behold, Moses and Elijah appeared to them, conversing with him. Then Peter said to Jesus in reply, "Lord, it is good that we are here. If you wish, I will make three tents here, one for you, one for Moses, and one for Elijah." While he was still speaking, behold, a bright cloud cast a shadow over them, then from the cloud came a voice that said, "This is my beloved Son, with whom I am well pleased; listen to him." When the disciples heard this, they fell prostrate and were very much afraid. But Jesus came and touched them, saying, "Rise, and do not be afraid." And when the disciples raised their eyes, they saw no one else but Jesus alone. As they were coming down from the mountain, Jesus charged them, "Do not tell the vision to anyone until the Son of Man has been raised from the dead." (Mt 17:1-9)
Jesus went up a high mountain. Usually when Jesus goes up any mountain it was for prayer and he always went alone. He never took anyone with him. This time he took with him three witnesses and he did not take all his disciples. This was a personal experience of Jesus (like prayer) yet it had to e witnessed to communicate something. And this communication should take place only after his resurrection.
There was transfiguration before the three of them. They saw a different face of Jesus. Till now they saw him like anyone of them. But now he appeared differently for them. The changes are compared to light and sun. His face was like sun. No one could look at his face directly. Again his clothes were white as light. Light is bright and it could not be seen directly. Jesus was other worldly person (not earthly let us say)
Rightly so there were two more persons talking to him and they were from the other world. There were with him Moses and Elijah. These were the proponents of belief in one true God. Moses had the experience of one true God on Mount Sinai and Elijah made the people to believe in one true God on Mount Carmel. Jesus joins these two on this mount to continue the same: he has come to reveal the one true God
