The Torah says (Behar 25:20-21), "If you will ask what shall we eat in the seventh year if we have not planted or gathered our produce, I will direct my blessing to you (i.e. to your land) in the sixth year, and it will provide for the three-year period." The Torah promises those who observe the laws of shemitah that the land will produce double or triple its normal yield in the sixth year, and that will last until they are able to plant and harvest once again. Why are those who observe shemitah rewarded with such an unnatural occurrence?
The Midrash Tanchuma (Vayikra 1:1) comments: "The strong warriors (giborei ko'ach) who do Hashem's bidding, to obey the voice of His word (Tehillim 103:20)"...
Rav Huna explained in the name of Reb Acha: this refers to Klal Yisrael who said na'aseh before nishma (and thus accepted to perform mitzvos before they heard what their obligation entailed). Reb Yitzchak Nafcha said: this refers to those who observe the laws of shemitah. And why are they called strong warriors? A person sees his field and his trees (being treated as if they are) ownerless, the fences are open, his fruits are being eaten, and he controls himself and does not protest. The Sages teach, "Who is a gibor - a strong person? One who controls his natural temperament. (Avos 4:1)"
The middah of gevurah involves controlling one's natural tendencies. One who overcomes feelings of anger or jealousy, or one who resists an improper desire for physical pleasure demonstrates inner strength. Such behavior is so fundamental to one's avodas Hashem that Rav Yosef Karo chose to begin his Shulchan Aruch (Orach Chaim 1:1) by alluding to this very idea. He writes, "One should be strong as a lion to rise up in the morning to serve his Creator" - echoing the statement of Reb Yehuda ben Teima (Avos 5:20) that one should be "strong as a lion to do the will of your Father in heaven."
