At the time of Joel's writing, locusts had just devoured the vegetation and crops of the people of Judah. As a result, their economy was suffering, many of the animals were without food, and their families were devastated physically and financially. This event was so severe that it was unlike anything that generation of people had ever witnessed.
Through this event, God was certainly getting the attention of His people in a big way, and He wanted them to be sure to convey what He was teaching them through this occurrence to their children and the generations of grandchildren that would come after them.
Have you ever experienced a season when you could tell that God was trying to get your attention? How did you respond?