What does Joel use to illustrate the need for repentance in Jerusalem?

The correct answer is the locust plague, which Joel uses as a vivid metaphor to illustrate the need for repentance in Jerusalem. In the context of the Book of Joel, the locust plague serves as a significant symbol of judgment and devastation that reflects the consequences of sin and disobedience among the people. Joel describes the devastation brought by the locusts in detail, using imagery that conveys the severity of their impact on the land, crops, and livelihoods.

This imagery is effective in communicating to the people that they must turn back to God and seek His mercy and forgiveness. The locusts represent not just a physical calamity, but also a spiritual wake-up call for the people to recognize their moral and ethical failings and to repent sincerely. Joel’s call for repentance is urgent, as he intertwines the physical consequences of the locusts with the spiritual need for the community to restore their relationship with God.

In comparison, other options like the plague of frogs, earthquake, or fire from the sky do not hold the same thematic significance within the context of Joel's message. These elements are not part of Joel's prophetic narrative and do not convey the same urgency for repentance in response to judgment as the locust plague does.