Charles Ellicott Commentary Joel 2:1

"Blow ye the trumpet in Zion, and sound an alarm in my holy mountain; let all the inhabitants of the land tremble: for the day of Jehovah cometh, for it is nigh at hand;" — Joel 2:1 (ASV)

Blow ye the trumpet.— The preaching of the prophet increases in its intensity. Behind the locusts, exemplified by them, there is a still more terrible visitation. He sees on the horizon a mustering of the nations hostile to his people, bent on destroying them.

Let the priests stir up the people for a fast, and for the defence of their land by the trumpet. The locusts have done their symbolical work; they have left their mark on the country. Now the day of Jehovah, the manifestation of His power, is approaching—it is imminent.