The narrator refers to the meeting as an assembling of the people. The verb is related to the noun qahal, assembly,
the word most often used in the books of Moses to refer specifically to the community of Israel gathered together for worship. So the narrator heightens our expectations that something good is going to happen, by suggesting that this gathering has a spiritual character.1
1 Then all the people of Israel came out, from Dan to Beersheba, including the land of Gilead, and the congregation assembled as one man to the LORD at Mizpah.