By contrast, the Earth (where objects seem to have motion only when moved) and things on it were composed of substances that were heavy and whose natural state was rest--thus the Earth was a "lazy" body that was not readily moved.
The Earth (where objects seem to have motion only when moved) were composed of substances. This was by contrast. Things on it were composed of substances. This was by contrast. These substances were heavy.--thus the Earth was a "lazy" body. This was by contrast. This body was not readily moved. Contrast's natural was rest.