This is a Medinan surah which refers to the main competing religious faiths of Muhammad's time and place (7th century Arabia): "the People of the Book and the idolators." These included Jews, Christians, and Arabian polytheists. The surah says that these groups "were not about to change their ways until they were sent clear evidence," which seems reasonable enough. Most people are hesitant to change their religious beliefs until they find compelling reasons to do so.
In the pre-scientific world of 7th century Arabia, "clear evidence" meant something quite different from what it means to secular 21st century people. It had nothing to do with the scientific method, empirical studies, and a rigorous academic community. For these people, "clear evidence" meant divine revelation. This is significant, and (I think) gets to the heart of the contemporary divide between religious and secular people. Secular folks (like me) require empirical evidence before we believe something. Religious folks (which still includes most people on the planet) are content with claims of divine revelation. This, to me, is weird, and suggests that religious faith is not about reason or logic, but about something deeper within human psychology.
