Of the prophet Joel almost nothing is known. No details of his personal life have come down to us. Even the time when he lived is not known with certainty, though it seems probable that he was one of the first of the prophets. From the frequent references to Judah and Jerusalem it would appear that he was a prophet of the Southern Kingdom.
   The general subject of his prophecy is divine judgment, or the Day of Jehovah. There is first a judgment  upon the Chosen People, inflicted through locusts. This is removed through fasting and intercession. A terrible day of final judgment embracing all nations is then described. The faithful will be rewarded while evil-doers will be punished. The fulfillment of one of Joel’s predictions by the scenes of the day of Pentecost, Acts 2:17-21, has given his book a prominent place in Christian thought. - Through the Bible Day by Day
Judah’s Judgment and Exaltation

I. The Infliction of Judgment, Joel 1:1-2:17
   1. An Unparalleled Brought and Locust Plague, Joel 1:1-7
   2. A Call to Lamentation, Joel 1:8-13
   3. A Call to Repentance, Joel 1:14-20
   4. The Sound of Alarm, Joel 2:1-11
   5. The Hope of Forgiveness, Joel 2:12-17 
II. The Manifestation of Mercy, Joel 2:18-32
   1. The Destruction of the Destroyer, Joel 2:18-20
   2. The Restoration of the Wasted Tears, Joel 2:21-27
   3. The Outpouring of the Divine Spirit, Joel 2:28-32
III. Judah and the Nations, Joel 3
   1. The Nations Summoned to Judgment, Joel 3:1-1-5
   2. The Exaltation of Judah, Joel 3:16-21 - Through the Bible Day by Day