The Transfiguration isn't just a matter of revealing who Christ is - it reveals our future. The Transfiguration is a brief glimpse of heaven, where we will behold Christ in all His Glory along with Moses and Elijah, and Peter, James, and John, and indeed, with all the saints. It is a visible depiction of the reality which we receive in the Supper.
We are not people of this World. Christ came into this world, to the Cross, so that He might take us to heaven. Would that we would remember this, especially when the world can be so tempting and distracting! Yes, Peter, James, and John must go down the mountain, but for a short time. Likewise, we toil here but only for a short time. We were created to experience the eternal transfiguration of the life everlasting. Christ Jesus truly is the light of the World!