Moses continues speaking to the people of Israel as if they were one man, so all instances of "you" are singular. (See: [[rc://en/ta/man/translate/figs-you]])
Here "voice" is a metonym for what a person says or a synecdoche for the whole person. AT: "he will not do what we tell him to do" or "he will not obey us" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-synecdoche]])