Joel calls for an alarm because “the day of the LORD is coming; it is near.” The trumpet announcement signals urgency and danger for the land. See Joel 2:1.
In Joel 2:1–3, a public alarm is ordered from Zion because a decisive “day of Yahweh” is near. The coming event is pictured as overwhelming darkness and as an unmatched, powerful force moving across the land. This unit stands at the start of Joel 2, intensifying the crisis described earlier in the book. After widespread devastation in chapter 1, the prophet now shifts from describing loss to sounding an urgent warning that something even more threatening is approaching.
Joel 2:1–3 presents an urgent, public warning centered on Zion (Jerusalem’s temple hill). The trumpet and alarm signal a crisis that concerns the whole community, not a private spiritual experience.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Joel 2:1, then read the surrounding section so the answer stays connected to the passage's flow.
1Blow you the trumpet in Zion, And sound an alarm in my holy mountain! Let all the inhabitants of the land tremble, For the day of Yahweh comes, For it is close at hand: