On Shabbat, the seventh day, we rest. We refrain from work, work often being understood as the act of creating something, or changing or altering something in a fundamental way. We refrain from creating in order to give our minds and our bodies an opportunity to rest, relax, and rejuvenate. Let's not forget that even God needed a day of rest after creating the world.
In this week's parsha, B'har-B'chukkotai, we learn about Shmitah. We learn that even the earth needs a rest. Millennia before scientific research confirmed the importance of crop rotation, ancient Israelites were giving their fields a rest from planting and harvesting every seven years. Their fields would lie fallow for an entire year during Shmitah. This is both a simple act and a profound sacrifice, especially when you think about the practical implications in an early agrarian society. This is a beautiful lesson to teach children, and one easily done by marking off a spot in the yard or garden and saying, "This part of the earth gets a rest this year. We won't plant anything; we won't pull any weeds. It can just do it's own thing. The earth works hard for us, and it deserves a break every now and then just like we do."