Adam Clarke on 2 Corinthians 3:13

And not as Moses - The splendor of Moses' countenance was so great that the Israelites could not bear to look upon his face, and therefore he was obliged to veil his face: this, it appears, he did typically, to represent the types and shadows by which the whole dispensation of which he was the minister was covered. So that the Israelites could not steadfastly look - could not then have the full view or discernment of that in which the Mosaic dispensation should issue and terminate.