But the people’s minds were hardened, and to this day whenever the old covenant is being read, the same veil covers their minds so they cannot understand the truth. And this veil can be removed only by believing in Christ. 15 Yes, even today when they read Moses’ writings, their hearts are covered with that veil, and they do not understand. NLT

Here is a great spiritual reality which we have to reckon with: although our message may be unveiled (i.e. clearly and boldly stated, vv.12,13), for the non-Christian people who hear it, there is a supernatural veil over their ”hearts” and ”minds”, so that they are unable to see the truth. Here Paul is writing specifically about the Jews, but in the next chapter, and verses 3-6, he says that this is true of all people. The language he uses is a little different, but he is undoubtedly writing about this same spiritual reality. He attributes the cause of the supernatural blindness to Satan, and he shows that it will take a miracle of God shining in the human heart to enable the sight of His glory ”in the face of Christ” (4:6). But God performs such miracles time and again. For both Jews and Gentiles the blindness can be removed. Sight is gloriously possible.

‘…since the problem which caused Moses to wear a veil in the first place was the state of the heart of the people, we can see that the veil still lies over the law itself, the ‘old covenant’, when it is read in the synagogue. In other words, the law really would reveal God’s glory; it really would point forward, like a great story in search of an ending, to the coming of the Messiah. But for those whose hearts are not ready for it, it is ‘veiled’. Tom Wright.

Jesus pointed out to the Jewish leaders of His day, however, that their blindness was wilful, and therefore culpable. Have a look at John 5:39,40;45-47.