“Earth” refers to the externals of a person or a community -- their everyday thoughts and actions -- in a broad, general sense. “Ground” refers to the parts of our external lives that are ready for cultivation, ready to be put to use. Cultivation, of course, involves loosening up the soil (breaking down our distracting habits and thoughts) and planting seeds (true concepts and ideas that spring from a desire to be good). As those seeds start growing, we begin to be truly useful. In short, then, “ground” in the Bible can mean a person or community that is receptive to the Lord's teaching. It can also mean a person or church that has received the Lord's teaching and is putting it to use.