The Second Rebellion (v. 39-45)
Being that nothing stands in the way of teshuvah (repentance), why were the Jewish people denied a second chance to enter the Land? Surely, they had repented for their sin, so why did Moshe say that their plan, "Will not succeed" (v. 41)?
From here we see that, while teshuvah does wipe away sin, both at the personal and the communal level, it does not guarantee a conquest could only succeed with the help of the Ark of the Covenant (see v. 44). And in our days, the land of Israel can only be fully conquered through the leadership of Moshiach - a person, "from the House of David, dedicated to the study of the Torah and observance of the mitzvos like his father David, according to the written law and the oral law, who will compel all the Jewish people to walk in it and strengthen its fences, and will fight the wars of God." (Rambam, Laws of Kings 11:4). Only through this path will the Temple be built and the exiles be gathered in.
(Based on Likkutei Sichos vol. 28, p. 327)