In Moshe’s final address to the nation, he informs them about the future and how they need to face their responsibilities:
ה’ אֱ-לֹ-הֶיךָ הוּא עֹבֵר לְפָנֶיךָ הוּא יַשְׁמִיד אֶת הַגּוֹיִם הָאֵלֶּה
1. As Moshe had demonstrated by, among others, Cheit HaEigel and the Meraglim, Moshe was willing to intercede on their behalf if they erred. His teffilos had halted deadly plagues and prevented their destruction. Fearful that they would err again in the future, they wondered – who would atone for their sins?
2. Bnei Yisrael would be waging wars to conquer Eretz Yisrael, and they worried how they would defeat their enemies without Moshe’s help, with his arms raised high in the air, ensuring victory as he did against Amaleik, and for leading the most recent victories over Sichon and Og…
L’havdil eleph alphei havdalos, Moshe Rabbeinu, always staying true to form as the most humble man to ever live, both comforts and teaches the nation – in his final address – about where everything came from: Hashem.
The same holds true for the battles that were won on the path from Egypt to Eretz Yisrael; Moshe was a conduit, but Hashem was behind everything and delivering our enemies into our hands.
Moshe then says that Yehoshua will now be the one who will fight for them, in both instances, but always know that the source of forgiveness and success is Hashem.
With so much in Parshiot Nitzavim and Vayeilech about teshuva, and the proximity of these parshiot every year to the Yamim Noraim, perhaps a lesson here is about an important focus during this time. Without taking an iota of importance or reverence from rabbeim or the chazzan leading slichot or any of the teffilot on Rosh Hashana and Yom Kippur, ultimately teshuva comes from Hashem. Teshuva cannot be attained only from listening to a good shiur or standing in shul listening to others. Those are incredibly important conduits and bridges to help us get to the proper place to daven for teshuva. A big chunk of our avodah, however, is a focus on our own personal teffilos and the meanings and feelings behind the words we say in davening. Assistance from others is amazing, but there has to be a level of our own effort.
Then in the next passuk Moshe calls to Yehoshua and tells him basically the exact same thing: 31:7-8
A beautiful example of our mesorah in action and of selfless encouragement, is found in virtually identical wording between Dovid HaMelech and Shlomo. Divrei Hayamim I, Perek 32 records Dovid speaking about Hashem prohibiting him from building the Beis HaMikdash. Instead, Shlomo, his son, would have that prestigious honor. Dovid tells his son, in Divrei Hayamim I 28:20:
Looks kinda familiar.