[3:137-138] Ways of life have passed away before you; so travel in the land and behold how was the end of those who denied. * This is an exposition for mankind, and a guidance, and an admonition for such as are God-fearing.
It means take a lesson from those who came before. Consider how We dealt with those who come successively, and how We took revenge on those who followed one after the other.
This is an exposition for mankind: an exposition to some people through rational proofs, to others through the unveilings to hearts, and to others through the self-disclosure of the Real in the innermost selves.