The book of Joel concerns the southern kingdom of Judah. Beyond that, we know nothing of Joel as a person—including nothing of when he lived or when the book was written. Some scholars have dated the book to the ninth century BC and others to the postexilic period (fifth of fourth centuries BC). The language of the book is very similar to what we see in other prophetic books, namely Amos, Micah, Zephaniah, Jeremiah, and Ezekiel. This does not help us date Joel, however, since it is unclear which books are dependent on others.
The main theme in Joel is the “Day of the Lord,” which refers to God’s coming judgment. This judgment is described as a locust invasion in chapters 1 and 2. Interpreters are divided as to whether these locusts are to be understood literally or symbolic of some foreign power, namely Babylon, Persian, Greece, or Rome. The nation in question would depend on the date of the book.
According to Joel, judgment will not only come on other nations, which was a false hope of the people of Judah. Rather, the day of the Lord will come to faithless Judah as well. However, with this said, restoration will only come after the judgment. This hope is uttered as early as 2:18, where Joel announces that God’s Spirit will be poured out on all, and so all will prophecy and see visions. We see this idea expressed again in the book of Acts (2:17-21) to describe the outpouring of God’s Spirit at Pentecost.
Restoration of Judah’s fortunes will also bring judgment to the nations, even those nations God used to judge Judah. God will punish them for their sins by bringing war upon them in the Valley of Jehoshaphat. This may be an actual valley named after King Jehoshaphat, or it may have symbolic value, since Jehoshaphat means “the Lord judges.”
Joel also uses apocalyptic language to describe the Day of the Lord: the sun and moon are darkened, the stars stop shining, the earth shakes, and the sky trembles. It might seem that Joel is speaking of the end of the world, but he is not. He is using graphic, cosmic language to describe events of great significance, not unlike today when we today of an “earth shattering” event.
– Peter Enns