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 the LORD cometh, for it is nigh at hand; Blow ye the trumpet in Zion - This verse also shows that the temple was still standing. All assemblies of the people were collected by the sound of the trumpet.
The day of the Lord cometh - This phrase generally means a day of judgment or punishment.