ועשיתם את חקתי ואת משפטי תשמרו ועשיתם אתם וישבתם על הארץ לבטח. ונתנה הארץ פריה ואכלתם לשבע וישבתם לבטח עליה. וכי תאמרו מה נאכל בשנה השביעת הן לא נזרע ולא נאסף את תבואתנו. וצויתי את ברכתי לכם בשנה הששית ועשת את התבואה לשלש השנים.
So you shall observe My statutes and keep My judgments, and perform them; and you will dwell in the land in safety. Then the land will yield its fruit, and you will eat your fill, and dwell there in safety. And if you say, "What shall we eat in the seventh year, since we shall not sow nor gather in our produce?" Then I will command My blessing on you in the sixth year, and it will bring forth produce enough for three years.After being promised that if we follow God's laws then we will have plenty of food, the Torah says that if we ask what will happen if we observe the shemitah (Sabbatical of the land) God will bless the land. Why would we ask that question? The Torah just told us that if we follow the commandments we will have plenty of food! Why the need for the further question and further blessing? It is redundant.
Click here to read moreR. Shlomo Wolbe, in vol. 2 of Alei Shiur, quotes R. Yisrael Salanter as saying that there is a debate between the Ramban and R. Bachya Ibn Pakuda (in his Chovos Ha-Levavos) regarding the need for effort (hishtadlus) in order to receive God's blessings. According to the Ramban one need only have faith in God while according to R. Bachya one needs to put in effort. R. Wolbe disagrees with R. Salanter's restatement of the Ramban's position and concludes, after a thorough analysis of the Ramban's writings on the subject, that the Ramban only says that one need not put in effort when one has a specific promise from God. Otherwise, even the Ramban would require you to extend effort in order to reap rewards.
According to the Ramban, those farmers who observe shemitah have a specific promise from God that they will have plenty of food. That could explain why there is the need for another promise. However, it does not explain why there is any additional need for people to ask how they will receive food.
According to R. Bachya, however, one can explain both the question and the answer. Receiving food as a reward for observing shemitah is unique in that shemitah is the only mitzvah that prevents people from doing hishtadlus in order to earn a living. Regarding all other commandments, a farmer who is to be rewarded for his fulfillment of them must still put in his effort to receive his reward. However, shemitah prevents a farmer from putting in effort. If that's the case, and he cannot do his hishtadlus, he might very well ask how he will eat in that year. There is no human action on which God's blessing can rest. That is why God has to give a special blessing that, in reward for observing shemitah, we will have plenty of food despite the lack of hishtadlus.