Predictability

"There are good reasons we left behind that existence [an existence lived close to the bone that daily experiences risk and daily remakes the circumstances of survival; an existence that binds people together with an urgent necessity that is also a satisfaction], but we left behind with it something essential, the forces that bind us to each other, to the moment, and to an inherent sense of purpose. The recovery of this purpose and closeness without crisis or pressure is the great contemporary task of being human. Or perhaps the dawning era of economic and environmental disasters will solve the conundrum for us more harshly." (A Paradise Built In Hell, Rebecca Solnit, 2009; page 113) 

That great task of being human is the problematic the Bible was designed to solve. The imposition of the periodic artificial disaster that is the sabbatical year is the simulation of crisis or pressure without having to suffer in the process an hysterical sense of catastrophe. The predictability of the sabbatical year allows the general public to choose and embrace the challenges of the disaster, and so to benefit from the opportunities for transcendance the 'calamity' would bring.