John Calvin Commentary Exodus 33:20

"And he said, Thou canst not see my face; for man shall not see me and live." — Exodus 33:20 (ASV)

And He said, You cannot see My face. Moses had indeed seen God's face before, but in such a mode of revelation as to be far inferior to its full radiance. Long before the birth of Moses, Jacob had said, I have seen God face to face (Genesis 32:30); and to Moses, as I have recently shown, a still clearer vision was granted.

Now, however, Moses obtains something better and more excellent; yet not so as to perfectly see God as He is in Himself, but only as far as the human mind is capable of bearing.

For although the angels are said to see God’s face in a more excellent manner than men, they still do not apprehend the immense perfection of His glory, by which they would be absorbed. God, therefore, justly declares that He cannot be seen by a mortal man, for we shall not see him as He is, until we shall be like Him (1 John 3:2).

For it must be that such incomprehensible brightness would reduce us to nothing. God, therefore, while He withholds us from a complete knowledge of Him, nevertheless manifests Himself as far as is fitting; indeed, tempering the amount of light to our humble capacity, He assumes the face which we are able to bear.