Although Hashem already made a covenant with the Jewish people by Matan Torah, 40 years later, He makes another one, as they’re about to enter the land of Eretz Yisroel. The first time He made it just with their soul, and that was enough to sustain them, however, the second time it was also with their body. This was because they were about to embark on a new life, where they would have to deal with realities of this physical world. In addition, that day was Rosh Hashanah, a day that we commemorate two things; firstly, the creation of man which was the purpose of the world, and second, the creation of the world itself. Ultimately man has to work on, not just himself, but also finding G-dliness and goodness in the world itself.

לקו״ש כד