The purpose of the gathering is for battle. This can be stated explicitly. Alternate translation: "gather yourselves together for battle" (See: [[rc://en/ta/man/translate/figs-explicit]])
Possible meanings are 1) Joel is telling the people of Judah that this is what they are to "proclaim among the nations" ([Joel 3:9](../03/09.md)) or 2) Joel interrupts the words of Yahweh and prays a short prayer.