We Are Not Individuals

Yom Kippur We Are Not Individuals  Why were the last two commandments given to the Jewish people, the Mitzvah of Hakhel and writing a Torah?  Why do we confess n Yom Kippur for sins we may have not even committed? and why would we say for the sins WE have committed?  Judaism gives a shared responsibility for one another, we are not individuals, but are part of a collective whole impacting each other in more ways you can imagine.