St. Thomas Aquinas (+1274) speaks of the Transfiguration (ST, III, Q. 45, art. 4, resp. 2) as a mystery of the "second regeneration". If I understand correctly, the first regeneration, the first rebirth, occurs for us in Baptism, when, by immeasurable grace, we are introduced into the divine life, i.e. into the very life of God. Our second rebirth, so to speak, will occur when are definitively introduced into the very life of God, the life of heaven.
In the Resurrection, Christ's body is definitively introduced into the life of heaven where "God will wipe every tear...Death will be no more; mourning and crying and pain will be no more, for the first things have passed away" (Revelation 21:4).The Transfiguration foreshadows this, and so is a mystery of the "second regeneration".
The Transfiguration reveals what awaits us. We look forward, at the Second Coming, to the "resurrection of the body" (Apostle's Creed), of our body, and thus to our whole person being definitively introduced into the life of heaven. As St. John says in his first epistle, (3:2) "we are God's children now; what we will be has not yet been revealed. What we do know is this: when he is revealed, we will be like him, for we will see him as he is".
And so, we look forward to unfathomable bliss in the whole of our person-glory (divine love overflowing) having irrigated every fiber of who we are. When Christ comes, and "all things are subjected to him, then the Son himself will also be subjected to the one who put all things in subjection under him, so that God may be all in all" (I Corinthians 15:28).When God is "all in all", then there is only light and love. In the meantime, we are given, in the midst of whatever we may be experiencing, foretastes of glory, in little, often hidden (sometimes very hidden!) ways: in the Eucharist, in our encounters with one another, in the bestowal of quiet blessings.Let us rejoice and be full of hope.
Yours in hope,