The Book of Joel is important as a prophetic oracle that foretells of the coming Day of the Lord that will bring God's final judgment upon the people of the earth.

His prophecy came at a time when Judah was experiencing prosperity and security, but God gave ample warning before the devastating judgment that was to come.

In chapter 1, Joel describes a terrible plague of locusts that brings destruction, followed by a severe famine throughout the land. He warns the people of Judah that devastation is going to sweep across the land, and he calls on the people of Judah and Jerusalem to weep over their sins and to fast and repent, because the day of the Lord is approaching. Yet if they will respond, there will be renewed blessings for the nation.

The plague of locusts does come and devastates the whole land like a storm. They darken the skies and destroy everything that was green, their fields of grain, vineyards, gardens, and trees.

In chapter 2, Joel prophesies of the coming Day of the Lord and he calls upon God's people to repent. Or, if they do not, they will be severely judged. Yet a promise of deliverance awaits in which God will restore the land if His people will repent. Return to me with all your heart with fasting, weeping, and mourning. Rend your hearts and not your garments. Return to the Lord your God for He is gracious and compassionate, slow to anger, and abounding in lovingkindness.

God promises, I will pour out my Spirit on all people. Your sons and daughters will prophesy, your old men will dream dreams, your young men will see visions.

The book then moves from historical events to prophesy about the end times when the world will be changed and when strange and frightening signs will appear.

In chapter 3, Joel prophesies of an outpouring of the Holy Spirit and judgment upon the nations. The Day of the Lord will be a period of judgment and restoration, first with judgment on God's people and then judgment on foreign nations, followed by purification and restoration of God's people through intense suffering.

Yet Joel also gave a promise of hope and spoke of great blessings that would follow in the kingdom of the Messiah.