The transfiguration's significance for Jesus has always seemed to be that he was getting the go ahead for his decision. But there also is significance for us in that Jesus still checked with God every step of the way to make sure he was doing God's will. If Jesus was doing that, then how much more should we?
It [the transfiguration] did something very precious for Jesus. Jesus had to take his own decisions. He had taken the decision to go to Jerusalem and that was the decision to face and accept the Cross. Obviously he had to be absolutely sure that was right before he could go on. On the mountain top he received a double approval of his decision.
(a) Moses and Elijah met with him. Now Moses was the supreme law-giver of Israel. To him the nation owed the laws of God. Elijah was the first and greatest of the prophets. Always men looked back to him as the prophet who brought to men the very voice of God. When these two great figures met with Jesus it meant that the greatest of the law-givers and the greatest of the prophets said to him, "Go on!" ...
(b) God spoke with Jesus. As always, Jesus did not consult his own wishes. He went to God and said, "What wilt thou have me to do?" He put all his plans and intentions before God. And God said to him, "You are acting as my own beloved Son should act and must act. Go on!"
The Gospel of Mark
(The Daily Bible Series, rev. ed.)