To his next rhetorical questions (here and in 1 Corinthians 11:15), Paul expects the answer Yes.
First, he points out that it is a disgrace for men to wear long hair. This is something that nature
—in other words, God’s creational order—teaches. Men naturally have less hair than women.
In Paul’s time, men (whether Jewish, Greek, or Roman) ordinarily kept their hair short. Long hair was worn only in exceptional circumstances, as when someone was in mourning or under a vow. The Corinthians would therefore find it easy to agree with Paul on this matter.
14 Does not nature itself teach you that if a man wears long hair it is a disgrace for him,