What does 2 Corinthians 3:10 mean?

Paul has compared the old covenant and the new covenant. He described the old covenant between God and Israel—defined by the Old Testament Law—as a "ministry of death" and a "ministry of condemnation." By that, he meant that the law at the heart of the covenant revealed to all who tried to follow it that they could not. All are sinners. None can reach God's glory through following the law (Romans 3:23). All stand condemned and sentenced to death and separation from God forever (Romans 6:23).

That old covenant did have glory at one point, though. It was, after all, the revelation of God on earth. The glory was reflected in Moses' face (2 Corinthians 3:7). Now, though, that glory that came with relationship with God through the law and the sacrifice of animals to cover sin has been surpassed by a far greater glory. This is the glory of the new covenant.

This covenant is God's offer of grace and mercy to all who trust in Christ and receive the gift of eternal life. God forgives the sin, once and for all, of everyone who believes that Christ's death covers their sin permanently. He gives the Holy Spirit to each believer, as well, as a promise of eternal glory to come.

Now that Christ has come and lived and died and has been resurrected, the old covenant is fulfilled. It offers no glory, at all, any longer. The glory of the new covenant outshines it so brightly as to make the reflected glory of the old covenant completely disappear.