Presence

I'm sure I'm missing something with Rashi's explanation of the connection between Shmittah and Har Sinai; to me it sounds like polemics. Ramban's explanation is more along the lines of what I was thinking. After the Golden Calf, Moshe had to convince God to continue his association with B'nei Yisrael. He was successful, but it didn't change the fact that, at this point, He would be "dwelling amongst them in the midst of their impurity." In order for this to happen, for God to rest his Presence among the flawed and imperfect community of Man, a system of separation had to be established between the Divine and the profane; this is Vayikra, which introduces the concept of repentance which enables Man to reestablish contact with the Divine, as well as the laws of holiness which delineate the separations, both constant and occasional, required to approach and coexist with the Divine. When this ground work is laid, when the system of barriers is formalized, we can then resume the narrative where we left off at Sinai, with the entrance into the land and related laws.