Fallow-ground is land left uncultivated until it becomes overgrown with thorns and weeds. Before sowing, the cultivator breaks it up and clears it so that the seed may grow.
The command to break up fallow ground in Hosea and Jeremiah figuratively calls people to abandon evil ways, repent, and clear their hearts so that the seed of righteousness may bear fruit.
Land was allowed to lie fallow so that it might become more fruitful, but the neglected field soon required cultivation and clearing before it could be sown again.