What does Exodus 31:13 mean?

Tell the Israelites, 'You need to keep my Sabbaths. This is a sign between me and you, for all generations, so you'll know that I'm the one who sets you apart as holy.' Exodus 31:13 - Modern Text Bible

(God tells Moses that the Sabbath isn't just a rule—it's a sign of the special relationship between God and his people, showing they're different because of him.)