John Gill Commentary Joel 2:15

"Blow the trumpet in Zion, sanctify a fast, call a solemn assembly;" — Joel 2:15 (ASV)

Blow the trumpet in Zion
For the calling of the people together to religious duties, which was one use of the silver trumpets made for and blows by the priests, (Numbers 10:2Numbers 10:3Numbers 10:8Numbers 10:10) ; sanctify a fast, call a solemn assembly; (See Gill on Joel 1:14).