Joel was written during the locust plague, a time of great distress for the people. The prophet sees in the devastation of the locusts an indication of the coming of the day of the Lord. Therefore all must repent with fasting and mourning. With repentance, however, there is a promise of relief and God’s blessing for Israel.

Joel 2

2:17 Let the priests, the ministers of the LORD, weep between the porch and the altar, and let them say, Spare thy people, O LORD, and give not thine heritage to reproach, that the heathen should rule over them: wherefore should they say among the people, Where is their God?