A bright cloud overshadowed them. The cloud spread over and around, not Jesus only and the other two, but in some degree over the apostles also, as St. Luke adds, "They feared as they entered into the cloud."
It was the Shechinah, the token of the presence of the Most High, who dwelleth in the unapproachable light. It enshrouded Jesus and his two companions, so that mortal eye could not pierce it or even look upon it; but the apostles, who were outside its immediate contact, were in some sort included in its influence, so that it could be said to overshadow them.
St. Peter calls it "the excellent glory ( τῆς μεγαλοπρεποῦς δο ìξης)" (2 Peter 1:17). The cloud from which on Sinai the old Law was given, was dark and threatening (Exodus 19:18; Exodus 20:21); this was bright, coming not to terrify, but to teach and to bless.
Here is seen the contrast between the two dispensations, the Law and the gospel (comp. Hebrews 12:18-24). A voice out of the cloud. It was the voice of God the Father, for he called Jesus, My beloved Son.
The same voice, saying the same words, had been heard over the waters of Jordan when Jesus was baptized (Matthew 3:17); it spake once again just before his Passion (John 12:28); at all times witnessing the Father's love and the perfect Divinity of Christ.
Now, as before, the Holy Trinity was revealed, the Father speaking with audible voice, the Son standing in radiant light, the Holy Spirit present with the intense brightness of the enveloping cloud. The words heard are fontal in the earlier Scriptures.
Thus in Isaiah 42:1 we read, "Behold my Servant, whom I uphold, my Chosen in whom my soul delighteth;" and in Psalms 2:7, "Thou art my Son; this day have I begotten thee." Hear ye him. Not Moses and Elias, but Jesus, the Mediator of a better covenant (Hebrews 8:6).
"This voice," St. Peter testifies, "we ourselves heard come out of heaven, when we were with him in the holy mount" (2 Peter 1:18). As Edersheim remarks, even if this Epistle is not St. Peter's, it still would represent the most ancient tradition.
"God, having of old spoken unto the fathers in the prophets, hath at the end of these days spoken unto us in his Son" (Hebrews 1:1). The command to hear him recalls the saying of Moses (Deuteronomy 18:15), that in good time God would raise up from Israel a Prophet like unto himself, and that unto him they shall hearken.