You are standing today, all of you, before Hashem your G-d: the leaders of your tribes, your elders and your officers, every man of Israel; your young children, your women, and your convert who is within your camp, your woodcutters and your water-drawers, so that you may enter the covenant of Hashem your G-d.
Every year we read Parshat Nitzavim on the Shabbat before Rosh Hashanah. The implication is that Parshat Nitzavim addresses the themes of Rosh Hashanah, and reading it enables us to experience the holiday properly.
In the first verses we read that the entire Jewish nation assembled to enter a covenant with G-d. The Torah mentions specifically that from the leaders to the water-drawers, all of Israel stood united as one -- "all of you."
What is the purpose of a covenant? If two friends are concerned that their relationship might sour at some point, they may enter into a covenant -- a pact to remain loyal to each other forever, even if future events or discoveries about one another cause them to lose favor in each other's eyes.
This, essentially, is the theme of Rosh Hashanah: a renewal of the covenant between G-d and the Jewish people. On Rosh Hashanah, when our love for G-d is strong (after our heartfelt teshuvah during the month of Elul), we commit ourselves to G-d unconditionally. We pray that G-d will enter this covenant with us, committing Himself to us unconditionally, even if later in the year our love may not be as obvious.
The covenant of Rosh Hashanah requires, however, that all members of the Jewish nation unite as one, just as the Jewish people did -- men, women and children, from the elders to the converts -- in Parshat Nitzavim. For in order to evoke G-d's unconditional commitment to us, we too must behave in a manner that transcends any reason or conditions. We do this by showing our sincere love and respect for all our fellow Jews, despite our understandable differences.