In an appropriate conditional construction, man means “whoever.” Consider the instructional example, “Whoever works diligently is more likely to succeed.” No one person is named; the expression can extend to each person who fulfils the stated condition.
This is a teaching example, not a Qur’anic quotation. It illustrates how singular-looking wording can operate generally. However, not every occurrence of man has the same function; interrogative and relative uses must also be understood in context.