A millstone is a stone used to grind grain. When grain is milled, two stones are actually used: the bed stone, or base, which remains stationary; and the runner stone, which turns on top of the base, grinding the grain.
In Bible times the millstone was a common item, and it is mentioned in several contexts in the Bible. The millstone was in fact so integral a part of society that the Mosaic Law forbade taking someone’s millstone in pledge (Deuteronomy 24:6). The millstone was needed to grind grain to make bread and sustain life, so taking someone’s millstone would be like taking his or her life in pledge.
A millstone was both extremely hard and exceedingly heavy, and it provided a vivid illustration for anyone who had experience with millstones. In the book of Job, God mentions the millstone in His description of a beast called Leviathan. This animal was so strong that God compared its impenetrable skin to a millstone: “Its chest is hard as rock, hard as a lower millstone” (Job 41:24). The “lower” millstone is the base stone upon which the upper millstone turns. A millstone was also chronicled as an instrument of death. A woman killed Gideon’s son Abimelech by dropping an upper millstone (the runner stone) from a tower. The stone landed on his head and crushed his skull (Judges 9:53; 2 Samuel 11:21).
Perhaps the most famous mention of a millstone in the Bible is in Jesus’ warning against leading His children astray. He said, “If anyone causes one of these little ones—those who believe in me—to stumble, it would be better for them if a large millstone were hung around their neck and they were thrown into the sea” (Mark 9:42). Causing a child of God to sin will bring severe judgment. If you would find it hard to swim with a millstone hanging around your neck, you should think twice before tempting God’s child.