The Prozbul

The books of Holiness and Devarim should be seen as early rabbinic commentaries on the Torah. As a case in point take the Prozbul of Hillel. In Devarim 15, the idea of Shmita is extended to loans. Hillel realized that this did not work, Devarim 15 had to be canceled. The mechanism of Prozbul does exactly this, and is an admission that Sefer Devarim is largely commentary, and not Torah per se.