What does Joel 2:11 mean?

The Lord shouts out in front of his army. His forces are huge, and his commands are unstoppable. The day of the Lord is massive and terrifying—no one can handle it. Joel 2:11 - Modern Text Bible

(God is leading this unstoppable force. The 'day of the Lord' is a time of reckoning, and it's so intense that nobody can stand up to it on their own.)