John Calvin Commentary 2 Corinthians 3:13

"and [are] not as Moses, [who] put a veil upon his face, that the children of Israel should not look stedfastly on the end of that which was passing away:" — 2 Corinthians 3:13 (ASV)

Not as Moses: Paul is not reasoning about the intention of Moses. For as it was his office to publish the law to his people, so there can be no doubt that he was desirous that its true meaning should be understood by all, and that he did not intentionally obscure his doctrine, but rather that the fault lay with the people.

Therefore, since he could not renew the minds of the hearers, he was content with faithfully discharging the duty assigned to him. Furthermore, the Lord having commanded him to put a veil between his face and the eyes of the onlookers, he obeyed. Nothing, therefore, is said here to dishonor Moses, for he was not required to do more than the commission that was assigned to him called for.

In addition to this, that dullness, or that weak and obtuse vision, of which Paul is now speaking, is confined exclusively to unbelievers, because the law, though wrapped up in figures, nevertheless did impart wisdom to babes, (Psalms 19:7).