What does 2 Corinthians 3:15 mean?

Paul has written that Israel's minds were hardened to the glory of God because of their own sinfulness. They could not, would not, receive His glory. Now Paul adds that the veil created by their own sin remains in place. This is true of the Israelites, who were opposing him, but Paul makes it clear that it is true of all who have not yet trusted in Christ for the forgiveness of their sin.

Paul had experienced what he was describing. He had been a highly regarded Pharisee in Israel. He had read every word of Moses' writing. He'd likely memorized a great deal of it. However, the veil of misunderstanding had remained over his own heart, until his sins were forgiven through faith in Christ and that veil was removed. Then, for the first time despite all his years of study and teaching, he could finally see and understand the glory of God in Christ.