In Vayikra 25: 20-22 (below) God says that he will guarantee a bountiful harvest if the Shmita is observed. Unlike other promises of spiritual reward, this one is easily quantifiable with observable ...
In Vayikra 25:3 it says: שש שנים תזרע שדך ושש שנים תזמור כרמך Why does it say twice שש שנים ?
Rashi says What does the subject of Shemittah have with Mount Sinai? Were not all the commandments stated from Sinai? However, [this teaches us that] just as with Shemittah, its general principles ...