John Gill Commentary Joel 2:12

"Yet even now, saith Jehovah, turn ye unto me with all your heart, and with fasting, and with weeping, and with mourning:" — Joel 2:12 (ASV)

Therefore also now, says the Lord. Before this terrible and intolerable day, which is near at hand, comes; before these judgments and calamities threatened take place, though just at hand; serious repentance is never too late, now is the accepted time; see (Luke 19:42–44) (2 Corinthians 6:2).

turn you [even] to me with all your heart; against whom they had sinned, and who had prepared his army against them, and was at the head of it, just ready to give the orders, and play his artillery upon them; and yet suggests, that even now, that if they turned to the Lord by true repentance, not feignedly and hypocritically, but cordially and sincerely, with true hearts, and with their whole hearts, he was ready to receive and forgive them. The Targum is, 'turn you to my worship with all your heart:'

and with fasting, and with weeping, and with mourning; external signs of inward grief and sorrow, testifying their hearty return to the Lord; which, though, without the heart, signify nothing, yet should be shown where hearty repentance is, for the honour and glory of God.