"The members of Jesus’ inner circle (Peter, James, and John), were eyewitnesses to the Transfiguration"
https://www.learnreligions.com/transfiguration-bible-story-summary-700068
"There He was transfigured before them. His face shone like the sun, and His clothes became as white as the light"
https://bible.org/seriespage/25-transfiguration-matthew-171-13
"The word “transfiguration” comes from the Latin roots trans- (“across”) and figura (“form, shape”). It thus signifies a change of form or appearance."
https://www.ncregister.com/blog/10-things-you-need-to-know-about-jesus-transfiguration
"Undoubtedly, the purpose of the transfiguration of Christ into at least a part of His heavenly glory was so that the “inner circle” of His disciples could gain a greater understanding of who Jesus was. Christ underwent a dramatic change in appearance in order that the disciples could behold Him in His glory. The disciples, who had only known Him in His human body, now had a greater realization of the deity of Christ, though they could not fully comprehend it."
https://www.gotquestions.org/transfiguration.html
"The Transfiguration was the glorification of the human body of Jesus. On this occasion His body underwent a change in form, a metamorphosis, so that it shone as brightly as the sun. At the time of the Transfiguration, Jesus' earthly ministry was coming to a close."
https://www.blueletterbible.org/faq/don_stewart/don_stewart_786.cfm
"The Transfiguration of Jesus (Matthew 17:1-13) is often being regarded as one of the most important miracles that took place during the course of the Savior’s earthly service (second only to the Resurrection). This miracle was meant to prove to the most loyal disciples of Jesus (Peter, James and John) that he was indeed the Son of God"
https://studycorgi.com/the-transfiguration-of-jesus-literary-criticism/