The Torah (VaYikra 25:1-7) teaches that every seventh year is shmittah and prohibits
working the land of Eretz Yisrael. During that year; one may not plow, plant, or work the
field in any way. Furthermore, the farmer must treat whatever grows by itself on his land
as ownerless, allowing others to pick and keep his fruit.
"The day of rainfall is as great as the day on which heaven and earth were created." The sages liken rain to the creation of the world: Just as the expression "gevura," might, is used in relation to Creation, so is it used in relation to rainfall.