We are all standing here today before G-d, about to enter the land of Israel and about to bring in the new year by declaring G-d's sovereignty over all of creation.
The messages of parashat Nitzavim are - entering a covenant with G-d, taking responsibility for ourselves and for one another, and acknowledging that the perfection of creation is in man's ability to do teshuvah - to return to G-d.
These are the very same messages of Rosh Hashanah, the awesome day on which all mankind stands before G-d and acknowledges that He is King and we are His beloved servants.