“Joel” means “The Lord is God” and the book bearing this prophet's name opens with Joel's description of a devastating plague of locusts invading the land. In the devastation and in the drought that typically follows such crop destructions, the prophet sees a sign of what it will be like in the “Day of the Lord,” a day of judgment for all who have ignored God and deviated from faithfulness to God's commandments. Locusts are a species of grasshopper that travel in enormous swarms capable of completely darkening the sky. They breed quickly and each stage of the insect's development (palmerworm, cankerworm, caterpillar, and full-grown insect) devours what the previous stage left behind. By this relentless means of attack they eventually devour all vegetation and leave the land bare, creating a truly life-threatening crisis for people and livestock whose existence depends on crops from the land. Joel uses this plague of locusts to summon the people to repent and “turn” their lives back toward God. He urges them to sanctify a solemn fast and to have the priests weep before God as the only means by which they can hope to experience future restoration and blessing from God (2.12-27). Once restored to God they will come to know a time when God's spirit will be poured out on everyone (2.28,29). Joel also foresees a time when God's judgment will come upon those nations which had conquered and occupied Judah and Jerusalem in the past (3.1-15). His final vision (3.16-20) is of God blessing the people with a restored and safe land.
This book may be the latest written of the prophetic books, if, as many think, 2.7-9 refers to the rebuilt walls of Jerusalem and 1.13,14 implies that the temple has been rebuilt and is once again the site of Israelite worship. The reference to Greeks in 3.6 also suggests a late date, perhaps a time in the years of the Persian Empire. Joel's vivid description of the signs of the coming Day of the Lord, especially of frightening portents in the heavens (2.30,31), establishes the essential template for what would become a standard feature in later apocalyptic writings.
The Devastating Swarm of Locusts and the Call to Repent (1.1—2.17)
The Promise of Restoration (2.18-27)
The Day of the Lord (2.28-32)
God's Judgment on the Nations and the Blessing of Judah (3.1-21)