12 That is why the LORD says, “Turn to me now, while there is time. Give me your hearts. Come with fasting, weeping, and mourning.”
On verses 12-17: The day of the Lord will be a dreadful day for those who have rejected God.
That is also why Joel implores his people to “return to the Lord your God, for He is gracious and compassionate, slow to anger and abounding in love, and he relents from sending calamity.” (v13) Echoing what God has already said in verse 12, Joel calls his people to fast (v15), to gather together (v15-16) and to pray and intercede for the people (v17) and to plead for God’s mercy.