Joel 2:11-15

11And the Lord shall utter his voice before his army: for his camp is very great: for he is strong that executeth his word: for the day of the Lord is great and very terrible; and who can abide it?

12Therefore also now, saith the Lord, turn ye even to me with all your heart, and with fasting, and with weeping, and with mourning: 13And rend your heart, and not your garments, and turn unto the Lord your God: for he is gracious and merciful, slow to anger, and of great kindness, and repenteth him of the evil. 14Who knoweth if he will return and repent, and leave a blessing behind him; even a meat offering and a drink offering unto the Lord your God?

15Blow the trumpet in Zion, sanctify a fast, call a solemn assembly: