What can shmita - the biblical sabbatical year and the agricultural cycle of which it is a key part -mean for the modern world? Abraham Isaac Kook, one of the giants of modern Jewish mystical thought, wrote this essay in 1909 to preface his book Shabbat Ha'aretz (Sabbath of the Land), in which he advocated new halakhic approaches to shmita in the context of the Zionist agricultural revival. His essay is a classic of authentic religious environmentalism, a meditation on the relationship between ancient legal structures and the deep spiritual life that they embody.