Joel 2:11 - Joseph Benson’s Commentary on the Old and New Testaments

And the Lord shall utter his voice before his army God, who can make the meanest parts of the creation the instruments of his vengeance, is here sublimely introduced, like a leader or general, commanding and animating this his army by his voice. For his camp is very great That is, his army is very great and terrible, making whatsoever havoc he orders them, and wheresoever. For the day of the Lord is great, &c. The time of God's particular judgments, as well as that of his general one, is commonly expressed by the day of the Lord, the former being an earnest and imperfect representation of the latter.