The prophet Joel speaks of a devastating locust plague (Joel 1-2). Beyond the literal destruction, what is the primary purpose of this prophetic imagery?

A To provide detailed instructions on how to combat insect infestations in ancient Israel. B To demonstrate Joel's knowledge of agricultural practices. C To call the people to repentance and warn them of a greater, impending judgment from God if they do not turn back to Him. D To predict a future economic crisis based on agricultural failure.