Ground Galvanization
The second Passuk describes Shemitta as שבתה הארץ שבת לד', to which Rashi explains, for the sake of Hashem, similar to Shabbos.
Netivot Shalom explains that the focus of creating the world, and likewise Eretz Yisrael was for the sake of Shabbos, and Shemitta. Hence, the Torah begins with the ideal, and then explains that one works the ground for 6 years, and rests on the seventh. Similarly, in the Aseret Hadibrot it first states to remember Shabbos, and then, speaks about working for 6 days.
Maharal - the number 7 is symbolic of the inner core. Items in this world exist in a 6-dimensional structure, and the 7th is the core that animates all the dimensions. Ohr Hachayim Hakadosh, every week the world becomes recreated in the merit of Shabbos. Likewise, by Shemitta, the ground gains another 6 years through keeping Shemitta.
What is the mindset one should have on Shabbat and Shemitta? 1. Hashem is the creator of this world; we are not the boss. We are living in Hashem’s world, and He gives us permission to live in it, as long as we abide by His laws. 2. Hashem is intimately involved in our lives, and we need to connect with this aspect of Divine Providence. [Hence, we hear so many stories of Hasgacha Pratit connected with farmers who keep Shemitta.].
R. Birnbaum in בקראי שמו explains, that one who keeps Shemitta should also have the mindset of appreciation to the ground, for all that it produces, and one wants to give it a rest. This sensitivity to an inanimate object is a reflection of our middos that emulate Hashem’s kindness. [He cautions one when throwing out clothes, or objects that one no longer needs, to wrap them up, and discard them with dignity.]