Albert Barnes Commentary Joel 2:21

"Fear not, O land, be glad and rejoice; for Jehovah hath done great things." — Joel 2:21 (ASV)

Fear not, O land - Before, they were commanded to tremble (Joel 2:1), now they are commanded, fear not; before, “to turn in weeping, fasting and mourning;” now, “to bound for joy and rejoice;” before, the land mourned; now, “the land is commanded to rejoice.”

The enemy had “done great things;” now the cause of joy is that God had done great things—the Almightiness of God overwhelming and sweeping over the might put forth to destroy.

It is better rendered, the Lord has done great things. If Joel includes in this God’s great doings yet to come, he speaks of them as, in the purpose of God, already in being; or he may, in this verse, presuppose that this new order of God’s mercies has begun, in the destruction of the pagan foe.