Why does Paul say nature teaches that long hair is a shame to a man?
Paul appeals to nature and the likely Roman custom of short cropped hair for men to argue that long hair on a man is a shame. He contrasts this with a woman's long hair, which is her glory and given as a covering.
Les explains that Paul tells the Corinthians to judge or discern for themselves whether it is comely for a woman to pray uncovered. Paul asks, "Doth not even nature itself teach you that if a man have long hair, it's a shame unto him?" Les thinks this goes back to the custom of Rome, where men wore rather short cropped hair. By contrast, if a woman has long hair, it is a glory to her, for her hair is given her for a covering and is a blessing. Les adds that Paul is tempering his correction; he does not want the Corinthians browbeaten or driven to rebellion, yet things must be straightened up. Chapter 14 will say everything in the local church must be done in order, not confusion, because God is a God of order.
Doth not even nature itself teach you, that, if a man have long hair, it is a shame unto him?