Matthew 17:5 (ESV) … “He was still speaking when, behold, a bright cloud overshadowed them, and a voice from the cloud said, “This is my beloved Son, with whom I am well pleased; listen to him.”
Peter was still bumbling on with his irresponsible nonsense when the brow of Hermon was suddenly wrapped with a cloud. That in itself was not unusual. A thick mantle of cloud often enfolds the summit of that mountain within minutes, only to disperse and disappear just as quickly. But this cloud was different. The text says it was “a bright cloud” and the implication is that it was the shekinah glory cloud. In Old Testament times that cloud once reposed on the mercy seat on the sacred ark within the holy of holies behind the veil. The shekinah was the visible token of God’s presence.
When the queen of England moves from Buckingham Palace to Windsor Castle, Sandringham, or Balmoral, the royal standard goes with her. When the flag flies over one of these residences, it means that the queen is there in person. In the same way the shekinah proclaimed God’s presence among His people. That glory had long since departed from Israel, but it appeared now to honor Jesus and to proclaim God’s personal presence on the mount.
Then came the Father’s voice putting an immediate end to Peter’s blundering remarks: “This is my beloved Son, in whom I am well pleased; hear ye him” (17:5). The same voice had said the same words at Jesus’ baptism (3:17). At that time the voice had endorsed the hidden years spent in private. Now it endorsed the years spent in public. God’s all-seeing eye had been on His Son night and day. The Father had rejoiced over Him and now proclaimed Him once more to be His well-beloved Son. Thus in the transfiguration the glory of Christ’s humanity was owned by God in the proclamation of Christ’s deity.
 Phillips, J. (2014). Exploring the Gospel of Matthew: An Expository Commentary (Mt 17:5). Kregel Publications; WORDsearch.