The Torah implies that one of the reasons for the terrible punishments described in our Parsha, including being driven out of Eretz Yisrael, is the failure to observe the Mitzvos of the Shemittah year (ויקרא כ"ו: ל"ד). As for those who do observe Shemittah, the Midrash quotes Rabbi Yitzchak Nafcha who explains a phrase in Tehillimק"ג: כ'( ) to apply to such people that observe Shemittah. The phrase refers to "מלאכיו," the angels of Hashem, and "גברי כח," strong warriors, who do Hashem's bidding and obey His word. Rabbi Yitzchak Nafcha says that it may be common for a person to perform a Mitzvah every day for a week or for a month, but not for an entire year. Yet this person, who observe Shemittah, lets his land become fallow and does not plant or sow for a whole year, accepting Hashem's will without saying anything. Can there be a greater angel or a more powerful warrior than he? We can also see the person's greatness from another perspective. A farmer may have spent years cultivating his orchard, but during Shemittah, he has no more right to his land than other people. This alone would explain why the people who observe this Mitzvah are described in Tehillim )שם( as warriors and angels.
However, if a person fails to observe the Mitzvah of Shemittah, a great punishment will come upon him. The Posuk earlier in our Parsha says "ואתכם אזרה בגוים והריקתי אחריכם חרב...," meaning, "and you, I will scatter among the nations and I will draw out the sword after you" (שם פסוק ל"ג). This indicates that if one fails to observe Shemittah, Hashem will punish him not only with exile, but with fear and death. Commenting on the next Posuk which says that the land will be appeased during all the days of its desolation, while the Jews are in the lands of their enemies, and will then be able to rest, Rashi (שם בד"ה את) says "שבעים שנה של גלות בבל הן היו כנגד שבעים שנות השמיטה ויובל," meaning that the seventy years of the Babylonian exile corresponded directly to the seventy years of Shemittah and Yovel which the Jews did not observe when they lived in Eretz Yisrael. Since the land did not rest when the Jews were there, it rested when they were not there. We thus see how the Mitzvah of Shemittah can elevate a person to be like an angel, if he is like a brave warrior who observes the laws properly, but it can also result in great punishment if it is not observed properly.