Rashi comments on the dots over “lanu ulvaneinu“ in “The hidden are for Hashem our G-d, vehaniglos lanu ulvaneinu la’asos es kol divrei haTorah hazos — the revealed are for us and our children to do all the words of this Torah.” (29:28) He quotes the opinion of R’ Nechemiah that with these words we accepted areivus zeh lazeh. That lanu, written in the plural, falls the responsibility for the known sins of individuals. The community is responsible for its members, even those who choose not to follow its goals. As parashas Nitzavim opens, “Atem nitzavim hayom kulkhem — You are standing here today, all of you.” The connection is made from the community in toward the member — and so membership is automatic, regardless of personal choice.
It is different but similar to a distinction The Rav makes between the am, and the eidah. The am is the community of fate (which would include all Jews) and the eidah (from the word eidus testimony, those who believe in and live according to the revelation in Sinai), the community of destiny. Man chooses to follow his destiny, fate is imposed upon him. Note the purpose of this second beris: “lema’an haqim osekha hayom Lo li’am, veHu yihyeh likha lEi-lokim — so that you will be established for Him a community of fate, and He will be for you a G-d.” (29:12)