It is a great shame, but you occasionally hear this referred to as an exceedingly mysterious event. In a sense it was, because it was so unusual, but really there is nothing mysterious in terms of what it teaches, when you put yourself in the place of the three disciples who witnessed it.
It's interesting that only three disciples were brought to see this great event. The Christian faith isn't a faith of miracles and visions bringing us into some relationship with God. Some people seem to think it is. They say, ‘If there is a God and if I'm going to come to know him or seek him, shouldn't I be getting visions or something? Shouldn't I be getting some fantastic appearances? Shouldn't I be receiving some out-of-this-world experiences?’ Some people think that. No, the Bible teaches otherwise. The Bible teaches that God, who is a great worker of miracles, has authenticated himself. He has authenticated his prophets in olden times, the apostles in the New Testament. Christ has vindicated himself by his miracles. Miracles in the Christian faith are for God and his inspired spokesmen in Bible times, so that the people could be clear that they really were speaking from God as they claim to be speaking. They were authenticated with amazing powers and Christ also, to prove his divinity, did amazing things. But the Christian faith is a faith which takes the message of God in a book and believes it and responds to the teaching of this book, which tells us how to be saved, how to seek the Lord, how to find him. When we obey it, we follow its instructions, we humble ourselves; when we repent of our sin and trust in Christ alone and what he's done on Calvary, then we find all the proof we need because he changes our lives and he makes himself known to us spiritually. But it isn't a faith of visions and seeing things and seeing spectacles and visions of this one and that one and so on. So only three disciples were selected for this special proof, not all of them.