Answer

Another מצוה we learn about in פרשת בהר is the מצוה of ______.

In ארץ ישראל, after working the land for six years, we let the it rest, as we do not do work on it during the seventh year.

Now, every Yid is part of the entire כלל ישראל. Since the nation as a whole has their שמיטה in the seventh year, the _______________ עבד עברי also has his personal release from servitude in his seventh year. (Understandably, the details of the general שמיטה year are quite different than the seventh year of the individual עבד עברי).