John Chrysostom

For since he said that in the reading of the Old Testament the veil remaineth, lest any should think that this that is said is from the obscurity of the Law, he both by other things showed even before what his meaning was, (for by saying, "their minds were hardened," he shows that the fault was their own,) and, in this place too, again. …

Homily 7 on 2 Corinthians ↗

Theophylact of Ohrid

Since he said above that a veil lies upon the reading of the Old Testament, lest anyone think that by the veil he means the obscurity of the law, he says: no, I call the veil the blindness and dullness of heart of the Jews. For even on the face of Moses it lay not for his sake, but because of the dullness and weak sight of the Jews.

Commentary on 2 Corinthians ↗

Thomas Aquinas

Then when he says, Yes, to this day whenever Moses is read a veil lies over their minds, he shows how even among the Jews the veil remains, as to unbelievers, although it has been removed by Christ. In regard to this it should be noted that a veil is said to be put on something in two ways: either because it is put on the thing seen, so that it cannot be seen; or because it is put on the one seeing, so that he may not see. But the veil was put on the Jews of the Old Law in both ways. …

Commentary on 2 Corinthians ↗