Why does Paul say let no man glory in men in 1 Corinthians 3:21?

Les explains that for a believer, education and a brilliant mind are fine and Christ honoring, but the issue is when an unbeliever places all faith in the wisdom of this world—it is nothing. Paul is driving at this contrast. He uses the analogy of Mars Hill, where Athenian philosophers called Paul a babbler, but in reality Paul had kernels of truth while the philosophers had only babble; the world has it upside down. In verse 21, since all of man's wisdom amounts to nothing without God's wisdom, therefore let no man glory in men, for all things are yours in Christ. This is Paul's whole premise: when we are in Christ, it makes all the difference. Thus glorying in men is excluded because human wisdom without God is empty, and in Christ all things are ours.