Blow the shofar in Zion!
Announce a sacred fast;
call a solemn assembly; Bible

“shofar.” The ram’s horn trumpet, not the metal trumpet. In this context, the shofar is blown to call for an assembly of the people, whereas in Joel 2:1 it was blown as a warning of the approaching army. The shofar was blown for different reasons, and so the reader has to be sensitive to the context to understand why it was blown.

Commentary for: Joel 2:15