Given the essential need to instruct the heads of the tribes about the conditions for 2.5 tribes setting east of the Jordan later in this Parasha, and that being a prime focus of this Parasha, the insertion of instructing the heads of the tribes in the first sentence was perhaps a device deemed beneficial for naming of the Parasha for its prime focus, “Mattot”.
This is certainly a more rabbinically-oriented suggestion, but perhaps there is a relationship between Moses telling the tribal heads here and the allowance for these vows to be dissolved by the court. Because making a vow is "like building a private altar" Moses needs to make sure those consequences are laid at the feet of the tribal chieftans, the officers who inaugurated the OG altar
Perhaps, but this doesn't help me understand why Moses never speaks to the tribal leaders on matters that are immediately relevant to them.
Given the essential need to instruct the heads of the tribes about the conditions for 2.5 tribes setting east of the Jordan later in this Parasha, and that being a prime focus of this Parasha, the insertion of instructing the heads of the tribes in the first sentence was perhaps a device deemed beneficial for naming of the Parasha for its prime focus, “Mattot”.
This is certainly a more rabbinically-oriented suggestion, but perhaps there is a relationship between Moses telling the tribal heads here and the allowance for these vows to be dissolved by the court. Because making a vow is "like building a private altar" Moses needs to make sure those consequences are laid at the feet of the tribal chieftans, the officers who inaugurated the OG altar