Aliya Summary: Moshe told the Jewish people that they have been given free choice to choose between good and evil, life and death. Their choice will determine whether they are the beneficiaries of G‑d’s blessings or curses. Moshe implored the Israelites to choose life. Moshe informed the people that he is 120 years of age on that day, and he is not permitted to cross the Jordan River together with them. Instead, Joshua will lead them, and G‑d will go before them and destroy their enemies. Moshe enjoined the Israelites to be strong and not fear their enemies.
From ou.org: The concept of Free Will is beautifully expressed in the concluding Aliya of Nitzavim. It marks the difference between human beings and all other creations. The sun and the moon “fulfill” G-d’s commands without conscious decisions. A bee doesn’t think things out and decide to pollinate a flower. Nor does a lion attacking a weak zebra evaluate the morality of his act. Only humans have the choice to do good or evil. G-d recommends and pleads with us to choose Life and Good, but He leaves the choice to us. That is why we are accountable for our actions; and that is why we stand before G-d in judgment on Rosh Hashana, while animals do not.