The prophet Joel, whose name means ‘Yahweh is God’, gives us no clue as to when and where he lived. I go with the hypothesis that he lived in Judah before the fall of Jerusalem, for he makes a number of references to Judah, Jerusalem and Zion.
Chapter 1 of the book opens with a locust invasion that was in all likelihood a historical reality. But this invasion is only a stepping stone to describe the invasion in chapter 2 of a large, mighty, disciplined and destructive army. It is unnerving to read in verse 11 that the Lord Himself is at the head of this second army, commanding it, and it His day.
The hinge on which the mood turns from gloom to hope is 2:12-17. In this section, God calls on His people to return to Him wholeheartedly. He will have compassion on His people, will drive back the besieging army, and will cause the land to be fruitful again, thus reversing the damage done by the locusts. Why? So that His people may know that He is Yahweh their God (2:27).
The section that follows, 2:28-32, is the most familiar passage in Joel in which God promises to pour out His Spirit on all believers without exception. The Lord also promises salvation for all who call on, and are called by, Him. I’m not sure if 2:31-32 refers to some past event, or to a future event, or indeed, both.
In 3:1-16a, God pronounces judgment on the enemies of His people.He will judge all those who oppose Him and reject His salvation. In 3:16b-21, He promises to redeem and restore His covenant people. He will be a refuge for them (3:16b) and will pardon their sin (3:21).
Sources: Mike Bullmore, Christopher Ash