Chelek 12, Behar 1

At the start of the Torah Portion of Behar, the Torah mentioned twice that during the Sabbatical year we should rest similar to how we rest on Shabbos.

Toras Kohanim learns a specific law based on the fact that we learn Shemitah from Shabbos and not Shabbos from Shemitah.

The rebbe explains that there is a foundational difference between Rashi and Toras Koshanim, Rashi is here to explain the meaning pertaining to comprehending the literal verse while Torah Kohanim is expounding the verse to learn a particular law.

We also talk about different expressions of holiness in a 'shabbos like world' and in a 'sabbatical year world'