It is not difficult to misunderstand what the Transfiguration of Jesus is about. Some of the prayers of the Mass for today's feast, at least as they have been translated into English, are likely to contribute to such misunderstanding.
In the prayer after communion, we tell God that he has 'revealed the true radiance of Christ in the glory of his transfiguration'. From this it might be easy to suppose that, at the Transfiguration, Peter, James, and John see Jesus as he really is, which is somehow different, and more true, than the way they see him normally. That is to say, in the Transfiguration, Jesus lets the mask slip, allows his real self, his divinity, to peep out, momentarily, from behind the veil of his apparently ordinary humanity. This way of thinking of the relationship between divinity and humanity in Jesus is sometimes mockingly described as 'space-suit' Christology: the humanity of Jesus is, at it were, the space-suit, which conceals the real Jesus, the divine Jesus, within itself.
However, if that is they way we think of Jesus, if that is what we think is being conveyed by the story of the Transfiguration of Jesus on the mountain, we will be wrong about both his humanity and his divinity. We get a better clue to what is going on at the Transfiguration from St Luke's Gospel than from St Mark's, because St Luke makes it plain that what Peter and James and John saw on the mount of the Transfiguration wasn't how Jesus really was at that time, but a prophetic vision of how he would be in the future.
It is clear that Elijah and Moses are the same two men who will greet the women at the empty tomb on the first Easter morning, and tell them that Jesus has risen; and that they are the same two men who, immediately after the Ascension of Jesus, will tell his disciples: 'this Jesus who has been taken up from you into heaven, will come in the same way as you saw him go into heaven'.
What Peter and James and John see on the mountain of the Transfiguration, then, is a vision of the glorious humanity of Jesus, risen from the dead, and ascended into heaven: not something hiding behind his humanity, but precisely his humanity glorified. And if they foresee the future, glorified, humanity of Jesus, then they also foresee their own future humanity, as it will be glorified with the same glory that is poured out on the humanity of Jesus.
The opening prayer of today's mass should have made this plain to us. The Word of God, who became human in Jesus of Nazareth, is co-equal with God the Father from all eternity: glorified together with the Father and the Spirit, as we say in the Creed. But in the life and death, the resurrection and ascension of Jesus of Nazareth the humanity we share with him is lifted up to share in the divine life and glory of the Holy Trinity. As the voice announces from the cloud in to-day's Gospel: 'This is my beloved Son, listen to him'. If we do listen to him then we are offered the opportunity to become co-heirs with him, sharers in his relationship with God, sharers in the glory of his perfected humanity.
But this comes at a price: 'He charged them to tell no one what they had seen until the Son of Man should have risen from the dead'. It is only after his death that the humanity of Jesus will be glorified in the resurrection and ascension.
And so it is with us. 'The sufferings of this present time' St Paul wrote in the letter to the Romans, 'are as nothing in comparison with the glory about to be revealed in us, for the creation awaits with eager longing the revealing of the children of God, when it will be set from its bondage to decay and will obtain the freedom of the glory of the children of God'. St Paul acknowledges that the sufferings of this present time are real: 'the whole creation has been groaning in labour pains' he says, 'and not only the creation, but we too, who already have the first fruits of the Spirit, we too groan inwardly' as we await that moment when our humanity will share completely in the glory which Jesus already has with the Holy Trinity.
On the mountain of the Transfiguration there was revealed the perfection of humanity that God intends for all of us, and the means by which we may attain to it: 'This is my beloved Son: listen to him'.