Mary, the mother of Jesus relates the event:

John, the disciple whom Jesus loved, rushed to my home. How I enjoyed seeing John, the youngest follower of my Son. Full of life and enthusiasm, ready in a moment to do whatever Jesus suggested, he came breathless and excited. “Mary, you’ll never imagine what Peter, James, and I just saw.” Those three special disciples, Mary thought, would mean something spectacular. “John, come in and tell me.” Though never doubting the wonders of my Son, I was surprised at this news. Jesus had taken the three up a mountain and was transfigured before them. His clothes became dazzlingly white, something my laundering could never do. Then a cloud came from the sky and a voice was heard: “This is my beloved Son. Listen to him.” Surely that was the voice of God, and John agreed. Listen. Listen to God. That is what I have been attentive to every day of my life. Though the voice of YHWH was silent, I listened to God in my heart. I “heard” through the Angel that the Lord was with me. Blessed was I, “a highly favored daughter.” I was His servant. I repeated my daily morning prayer in the presence of the angel: “Let it be done.” John continued his story. Moses and Elijah were there. How glorious! John claimed the three  disciples were ready to build tents. . .  until the conversation “spoke of his passage, which he was about to fulfill in Jerusalem.”  John looked down. He had said too much. Mary gasped but caught her breath as she saw the distress in John’s eyes. John admitted that he had said something they were not going to tell anyone. But surely his mother needed to know. Perhaps she had already intuited the importance of the event. Simeon had told her three decades earlier that her heart “would be pierced with a sword.”