As in Old Testament times, Jesus has gone up the mountain to meet with God, in the company of some of the apostles, to speak with God, as happened precisely to Moses and Elijah, who were also present on the mountain that day of the Transfiguration of Jesus. This manifestation of the divine wants to connect the entire ancient biblical world, the Law and the prophets, who are represented in the persons of Moses and Elijah, with the glorious manifestation of God in the person of Jesus Christ. Jesus is the awaited Messiah, the Savior, the Promised One from ancient times. In Jesus the promises that God has given to humanity since ancient times are fulfilled.
Today's second reading (2 Peter 1: 16-19) is precisely Peter's written testimony about this meeting on the Mount of Transfiguration. Peter himself will say: “We did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we had been eyewitnesses of his majesty. For he received honor and glory from God the Father when that unique declaration came to him from the majestic glory, "This is my Son, my beloved, with whom I am well pleased." We ourselves heard this voice come from heaven while we were with him on the holy mountain."
Peter can only bear witness to what he experienced, since he consciously experienced it first-hand. Like Peter, each apostle of Jesus will know how to give his life until death, through martyrdom, misunderstanding, rejection, exile to defend the truth that is in Christ.
It is clear that if it is God the Father who presents the Son, Jesus is the Son of the Father, and Jesus is One with the Father, and definitely Jesus is God. This revelation of the divine caused astonishment and fear among the witnesses of that day; however, Jesus knew how to calm the souls of his own. And once again, faced with the temptation to stay in that instant and make that moment an eternity (as Peter said: "Lord, it is good that we are here."), Jesus brings them back to reality, they must come down from the mountain to meet humanity and give them the Truth that will set each and every one of them free: Jesus Christ, the beloved Son, in whom God the Father is well pleased.
P. Carlos Flores, OSA