Luke 9:34

(in Matt. tom. 12.) Now His disciples being unable to bear this, fell down, humbled under the mighty hand of God, greatly afraid since they knew what was said to Moses, No man shall see my face, and lice. Hence it follows, And they feared as they entered into the cloud.

(in Esai. c. 4. 5.) For the obscurity of the Law had passed away; for as smoke is caused by the fire, so the cloud by light; but because a cloud is the sign of calmness, the rest of the future state is signified by the covering of a cloud.

For it is the overshadowing of the divine Spirit which does not darken, but reveals secret things to the hearts of men.

And mark, that as when our Lord was baptized in Jordan, so also when He was glorified on the Mount, the mystery of the whole Trinity is declared; for His glory which we confess at baptism, we shall see at the resurrection. Nor in vain does the Holy Spirit appear here in the cloud, there in the form of a dove, seeing that he who now preserves with a simple heart the faith which he receives, shall then in the light of open vision look upon those things which he believed.

But while Peter spake, our Lord builds a tabernacle not made with hands, and enters into it with the Prophets. Hence it is added, While he thus spake there came a cloud and overshadowed them, to show that He was not inferior to the Father. For as in the Old Testament it was said, the Lord dwelt in the cloud, so now also a cloud received our Lord, not a dark cloud, but bright and shining.