Mark 9:7

And there came a cloud overshadowing them: and there came a voice out of the cloud, This is my beloved Son: hear ye him.

What is meant by the overshadowing cloud? Did it envelop all of the group or only Jesus, Moses, and Elijah? From the fact of God's presence in the Old Testament having been indicated by the pillar of a cloud by day (Exodus 13:21), as well as from other associations of clouds with the presence of God (Psalms 79:14; 1 Thessalonians 4:17, etc.), there is a strong inclination to make the same association here; but a comparison with the baptismal scene (Matthew 3:16,17) in which Christ as the Son of God, the Spirit as a dove, and the voice from the Father indicate the presence of the Trinity, suggests that the same is in view here. If so, Christ as the beloved Son and the voice from the Father would leave the overshadowing of the cloud as a symbol or manifestation of the Holy Spirit. This is not indicated absolutely, however, because the voice was said to have come "out of the cloud." In Luke 1:35, the coming of the Holy Spirit upon Mary was linked with the statement that the power of the Most High would "overshadow" her.

Regarding the question of who was overshadowed, Cranfield, arguing from the premise that the disciples seemed to have been addressed outside the cloud, concluded that the enveloping included only Jesus, Moses, and Elijah.[8] Cranfield is wrong, for Luke records that "they feared as they entered into the cloud" (Luke 9:34).

Hear ye him ... These words indicate far more than a mere admonition to pay attention. As in Deuteronomy 18:15, they carry a very strong meaning, "Hear and obey."[9] In context, they also have the equivalent meaning of "Do not hear Moses or Elijah, but hear Jesus only." Thus, Christians are released from any necessity of obeying Mosaic or prophetic requirements found in the Old Testament.

[8] C. E. B. Cranfield, The Gospel according to Saint Mark (Cambridge: University Press, 1966), p. 292.

[9] Ibid.