Peter is being interrupted by God himself, who reveals himself in a bright cloud: the kind with which God adorns himself when revealing himself on earth (Exodus 16:10, Exodus 19:9, Exodus 24:15–18, Exodus 33:9–11; 1 Kings 8:10). A similar cloud appears in Israel’s exodus in the desert and when Solomon consecrates the temple. Such a cloud also takes people into heaven (Acts 1:9; 1 Thessalonians 4:17; Revelation 11:12). When overshadowed by a cloud, one can see nothing, and can only hear, putting the stress on the Word of God alone, as Moses did when stressing to Israel that they saw no form, but only heard a voice, on Sinai.
Even before Peter has finished speaking, he is interrupted by God himself, who—as in the past—here reveals himself in a bright cloud. This is, in other words, not a rain cloud, but the kind of bright cloud with which God adorns himself when revealing himself on earth (see Exodus 16:10, Exodus 19:9, Exodus 24:15–18, Exodus 33:9–11; 1 Kings 8:10). A similar cloud also appeared during Israel’s exodus in the desert and again when Solomon consecrated the temple. We also read about a cloud that proceeds to take people up into heaven (Acts 1:9; 1 Thessalonians 4:17;, Revelation 11:12).1
In being overshadowed by a bright cloud one sees nothing anymore and can only hear as one is surrounded by mist. This creates the right atmosphere for the emphasis to fall on the Word of God alone, as Moses made clear when stressing to Israel that they saw no form, but only heard a voice, on Mount Sinai.2
5 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.”