A cloud is a common Biblical metaphor for God, and an apt one. For example, when Moses re-climbed Mt. Sinai to get the second set of tablets, "the LORD descended in the cloud and stood with Moses there." (Exodus 34:5)
A cloud is an apt image for God because a cloud both reveals and conceals. If one is walking or driving in a heavy fog, one is very aware of the presence of the cloud. The cloud is very real. At the same time, being in the midst of the cloud does not enable one to fully see and understand the cloud.
Have you had an experience of being in the presence of God? Such experiences are often very real to us, yet difficult to put into words—kind of like a cloud.
God of mystery, envelop me like a cloud, that I may be certain of your presence. Amen.
Luke 9:28-36 (NRSV)
28 Now about eight days after these sayings Jesus took with him Peter and John and James, and went up on the mountain to pray.
29 And while he was praying, the appearance of his face changed, and his clothes became dazzling white.
30 Suddenly they saw two men, Moses and Elijah, talking to him.
31 They appeared in glory and were speaking of his departure, which he was about to accomplish at Jerusalem.
32 Now Peter and his companions were weighed down with sleep; but since they had stayed awake, they saw his glory and the two men who stood with him.
33 Just as they were leaving him, Peter said to Jesus, "Master, it is good for us to be here; let us make three dwellings, one for you, one for Moses, and one for Elijah" --not knowing what he said.
34 While he was saying this, a cloud came and overshadowed them; and they were terrified as they entered the cloud.
35 Then from the cloud came a voice that said, "This is my Son, my Chosen; listen to him!"
36 When the voice had spoken, Jesus was found alone. And they kept silent and in those days told no one any of the things they had seen.