Joel wrote to warn his audience about a coming day in which God would judge His people. He compared this devastating judgment to a terrible locust invasion that had fairly recently swept through the land. What he said about this coming judgment has only seen partial fulfillment; some of it still lies in the eschatological future. God would send blessing as well as judgment, however, and this too has only come partially on the Israelites so far. The prophet warned his hearers that unless they repented of their empty formalism in worship and turned back to Yahweh wholeheartedly, devastating judgment would overtake them. If they repented, God would pardon them and restore His blessings to them abundantly.
