Catechism of the Catholic Church §555 — excerpt
For a moment Jesus discloses his divine glory, confirming Peter's confession. He also reveals that he will have to go by the way of the cross at Jerusalem in order to "enter into his glory".
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. Thomas Aquinas, STh III, 45, 4, ad 2 · Byzantine Liturgy, Feast of the Transfiguration, Kontakion