When you shall come to the land that I am giving you, and the land shall rest, a rest for Hashem.
The Ohr Hachaim asks, what does this possuk teach us? The next possuk will tell us שֵׁש שָׁנִים תִזְרַע שָׁדֶךָ...... וּבַשָׁנָׁה הַשְבִיעִת שַבַת שַבָׁתוֹן – six years you shall sow your fields....and in the seventh it shall be a complete rest. This teaches us that we may not work in the fields during the Shemittah year. What does the Torah add with the commandment of rest in the first possuk that was not already included in the second?
The Ohr Hachaim derives from here that the Torah is teaching us a new understanding behind the mitzvah of Shemittah. The land that Hashem gave Klal Yisroel was not given to them completely and unreservedly. Hashem reserved the Shemittah year for Himself, and Klal Yisroel has no right to plant or cultivate the land this year. The possuk now reads כִי תָׁבֹאוּ אֶל הָׁאָׁרֶץ אֲשֶר אֲנִ י נֹתֵׁן לָׁכֶם – when you shall come to the land that I am giving you, know that I am only giving it to you without the rights of the resting year. In that year וְשָׁבְתָׁה הָׁאָׁרֶץ שַבָׁת לַה' – the land shall rest for Hashem. That year was reserved for Hashem, and the planting rights still belong to Him. The gift of the land excluded whatever concerns this year of rest.
The Ohr Hachaim adds that Hashem could have conditioned the gift of Eretz Yisroel on Klal Yisroel’s guarding the laws of Shemittah. If they follow the laws of Shemittah, the land is theirs. If they don’t, He will take it away from them. He did not need to make this clause by reserving that year's ownership for Himself.
However, in that case, if Klal Yisroel neglected this Mitzvah, they would lose their entire rights to Eretz Yisroel, and the gift would be nullified. Hashem wished the gift to last, and He merely wished to reserve this right for Himself. For this reason, when Klal Yisroel sadly neglected their Mitzvah, their punishment was that they went into exile, and during those years, the land rested. They owed those years of rest to Hashem, and they returned it. Afterward, they returned to the Land. However, the gift of Eretz Yisroel could never be reversed or nullified.
