What does Exodus 10:8 mean?
Under threat (Exodus 10:1–6) of an eighth disaster (Exodus 7:21; 8:6, 17, 24; 9:6, 10, 24), Pharaoh's advisors convince him to negotiate with Moses. They realize that if locusts consume what little is left of vegetation and food stores, they will face starvation (Exodus 10:7). Yet neither Pharaoh nor his servants seem willing to give the Lord exactly what He has demanded: release of the Israelite people.Pharaoh hopes that giving the Israelites a little room for religion might allow Egypt to keep their slaves (Exodus 1:11–14). Of course, Egypt's king would assume the same thing everyone else would: once the slaves all leave, they aren't coming back. He assumes that those who leave will not abandon family members who are still in captivity. So, he suggests that only a certain group of Israelites be released. This is not a negotiation to release slaves, it is only a negotiation to stop the plagues.
Moses' first request to Pharaoh was for the Israelites to go three days away in order to worship God (Exodus 3:18; 5:3). The Lord knew that Pharaoh would never agree to this request (Exodus 3:19–20), let alone complete freedom. God is demanding that the people be freed in order to worship, or "serve," which really means being freed entirely. Moses will rule out Pharaoh's lesser option immediately (Exodus 10:9).