The decree of the shemitta year might have been a very harsh restriction when issued. The Jews were told that they could not work on their fields for an entire year. The wild grown produce would not belong to anybody by right, and the land and it's products belonged to Hashem and no one else.
Many questions arise on this decree. Why does this apply every 7th year? How would the Jews provide food for themselves during the Shemitta year?
The answer to these questions can be seen through the number seven. The number seven is used in Jewish life very often. Paroh dreamed of the seven fat cows and the seven skinny cows. Yehoshua circled the walls of Yericho seven times. Many Korbanot required that the Kohen dip his finger in the blood and sprinkle it seven times. When a Chatan and Kallah get married, the Kallah circles the Chatan seven times under the Chupah, with seven Berachot. A mourner does not engage in any public activity for seven days. The prime example of this is Shabbat which is on every seventh day of the week. This reminds us that our souls are of divine nature. The Shemitta year is of similar nature. Shemitta reminds us that everything that we own belongs to Hashem. Whatever we own is given to us by Hashem for temporary possession. For example: Money. We are given money, but it is really a loan, and we have to see that some of it is used for charity. Similarly when we are given land we have to see that some of it is given to poor people. If we forget that we are only given these things temporarily, then we forget Hashem's omnipotence. The Shemitta year, when we have ownership of the land makes sure that we remember.