“huge millstone.” The Greek literally reads, “millstone of a donkey,” and it refers to the large commercial millstones, which weighed many hundreds of pounds and were turned by donkeys or oxen; see commentary on Mark 9:42.
“the lake.” The “sea” of Galilee is actually quite a small lake, only 7 miles (11.2 km) across and 12 miles (19.3 km) long, and the entire lake can be seen from the escarpments on both the east and west sides. The Greek word thalasso, lake, sea, or ocean, does not really refer to the size of the body of water, and thus has to be translated into the English “lake,” “sea,” or “ocean” by knowing the body of water that is being referred to (see commentary on Matt. 4:18). The name, “the Sea of Galilee,” was given by people who had never seen it. It is actually quite a small lake. Using “the sea” here makes Jesus’ statement much more general and removes it from its geographical context.