Since the fall of Jerusalem to Babylon, the Jews in exile had been observing a series of fasts in memory of all that had happened to them.
It's not too late to restore relationships, to repair bridges, to pray for and say yes to new opportunities. God can make up for all you didn't do right before, He can more than make up for it! Knowing that God will restore what was lost, what was wasted, frees you and me to move into and with God's will now—to fulfill His purpose for us today.
Fasting can bring breakthrough in the spiritual realm that will never happen any other way. So Joel called God's people together to fast and to pray.