Adam Clarke on Judges 20:2

The chief of all the people - The corners פנות pinnoth; for as the corner-stones are the strength of the walls, so are the chiefs the strength of the people. Hence Christ is called the chief corner-stone.

In the assembly of the people of God - The Septuagint translate, And all the tribes of Israel stood up before the face of the Lord, εν εκκλησιᾳ του λαου του Θεου, in the Church of the people of God. Here was a Church, though there was no priest; for, as Tertullian says, Ubi tres, ecclesia est, licet laici; "Wheresoever three are gathered together in the name of the Lord, there is a Church, although there be none but the laity."