Joel 2:1

Blow ye the horn in Zion see, in justification of this rendering of shôphâr, on Amos 2:2. The hornis to be sounded, in order to give notice of impending danger, and arouse the people to meet it (cp. on Amos 3:6).

sound an alarm The word, though it often has the sense of shouting, is used also to denote the long, continuous blast of the horn, which, in contradistinction to a succession of short, sharp notes, was the signal of danger (Numbers 10:9, though the reference there is not to the shôphâr, but to the ḥatzôtzerâh).

tremble aroused viz., by the -alarm," from their security.

for the day of Jehovah cometh, forit is at hand (or near)] Repeated, with some variation, from Joel 1:15. at hand(or near), exactly as Joel 1:15; Joel 3:14.