"Bless Adonai, O God's angels, mighty beings who do God's bidding, ever obedient to God's bidding" (Psalms 103:20) Who is this verse referring to when it mentions mighty beings? Rabbi Yitzhak says, those who observe the shmita year. It is the way of humanity to observe a commandment for a day, a week or even a month, but for a whole year?! But during the Sabbatical Year, when people see their fields and vineyards opened up to the world, and their produce consumed by whoever needs it, and they allow this to happen, there is no mightier being than this!
Rabbi Abraham Isaac Kook's Introduction to Shabbat Ha'Aretz, translation by Rabbi Julian Sinclair:
What Shabbat does for the individual, shmita does for the nation as a whole...the soul of the people and the land intertwine, working from the basis of their being to bring into existence the intricate patterns of inner holiness that lie within them during the sabbatical year. The people works with its own soul force on the land, and the land works on the people, refining their character in line with the divine desire for life inherent in their makeup. The people and the land both need a year of Sabbath!
Wendell Berry, The Unsettling of America (1977):
We have given up the understanding...that our land passes in and out of our bodies just as our bodies pass in and out of our land; that as we and our land are part of one another, so all who are living as neighbors here, human and plant and animal, are part of one another, and so cannot possibly flourish alone; that, therefore, our culture must be our response to our place...
There are very good reasons to rotate crops. Rotating crops usually means fewer problems with insects, parasitic nematodes, weeds and plant diseases.