The whole congregation of the Lord refers to all the western tribes: Judah, Benjamin, Ephraim, Dan, Naphtali, Manasseh, Issachar, Simeon, Zebulun, and Asher. Presumably the Levites also joined the gathering. Of interest is the fact that this gathering is referred to as the whole congregation of the LORD
even though it does not include Reuben, Gad, or the other half of Manasseh.
16 “Thus says the whole congregation of the LORD, ‘What is this breach of faith that you have committed against the God of Israel in turning away this day from following the LORD by building yourselves an altar this day in rebellion against the LORD?