Charles Ellicott Commentary Joel 2:13

"and rend your heart, and not your garments, and turn unto Jehovah your God; for he is gracious and merciful, slow to anger, and abundant in lovingkindness, and repenteth him of the evil." — Joel 2:13 (ASV)

He repents of the evil— that is, in the sense that of His own will He does not will the death of a sinner. The judgments of God, like His mercies, are conditional. As the Lord repented that He had made Saul king over Israel (that is, grieved), and revoked the appointment, so now He repents of the evil that will fall on His people if they are unrepentant. If they will repent, perhaps He will not do it.