The Biblical prophets knew that everything is temporary in our world. In every event threatening the lives of the people, they saw the coming of the Lord who judges this world in order to establish the final world.
Joel speaks when the land is invaded by locusts. The people are looking at their ruined fields and their lost crops. Joel looks beyond: The day of Yahweh is exceedingly great, terrible and dreadful – who can endure it?
Along with the promise of freedom from this plague, God also promises a happy age in which there will be neither grief nor fear. A day is announced when God will give the Spirit of the prophets to all his children: for the church, Joel is the prophet who announced Pentecost, as Peter said on that day (see Acts 2:17).