"...For the day of the Lord is coming...a day of darkness and gloom, a day of clouds and thick darkness...a fire consumes before them, and behind them a flame burns...before them the people are in anguish; all faces turn pale...Before them the earth quakes, The heavens tremble, the sun and the moon grow dark, and the stars lose their brightness. And the Lord utters His voice before His army... strong is he who carries out His word. The day of the Lord is indeed great and very awesome, and who can endure it (Joel 2:1-11)."
In the aftermath of a horrible locust plague that destroyed everything, the prophet begins to describe the day of the Lord. The day of the locusts came, and they destroyed everything. The day of the Lord is coming, and he will swarm the earth with the armies of Heaven and consume the land and all its inhabitants. Compared to the day of the Lord, the locust plague will seem insignificant.
God typically would rather not execute his great wrath. His warnings are typically calls for his people to return to him. Notice what he says next.
"Yet even now, declares the Lord, Return to Me will all your heart, and with fasting, weeping, and mourning; and rend your heart and not your garments. Now return to the Lord your God, for He is gracious and compassionate, Slow to anger, abounding in lovingkindness, and relenting of evil. (Joel 2:12-13)."
An ancient near-eastern custom of mourning, regret, or anguish was to tear your garment. However, God is not interested in mere outward acts. He has always been interested in the heart. He says to rend your heart, not your garments. If so, the text says he relents. In like manner, Jeremiah tells the people to circumcise their heart (Jer 4:4). Paul takes up the same message in Romans 2:29. True circumcision is of the heart, of the Spirit, not of the letter.
God's goal is not shame, but joy in the Lord. There is vindication in repentance. The Lord raises up those who have rent their hearts.
"Do not fear, O land, rejoice and be glad ... in the Lord your God; For He has given you the early rain for your vindication...The threshing floors will be full of grain, And the vats will overflow...I will make up to you for the years That the swarming locust has eaten, My great army which I sent among you. You will have plenty to eat and be satisfied. And praise the name of the Lord your God, Who has dealt wondrously with you; Then My people will never be put to shame. Thus you will know that I am in the midst of Israel, And that I am the Lord your God, And there is no other; And My people will never be put to shame (Joel 2:21-27).
It would be a good idea if we had more prayer services where we not only praise the Lord and give him thanks, but also confess and mourn. "Weeping may last for the night, But a shout of joy comes in the morning (Ps 30:5)."