'Exo 3:18 And they will listen to your voice, and you and the elders of Israel shall go to the king of Egypt and say to him, ‘The LORD, the God of the Hebrews, has met with us; and now, please let us go a three days’ journey into the wilderness, that we may sacrifice to the LORD our God.
The context of Exodus 3:18 is Moses’ conversation with God. God tasks Moses with going to the King of Egypt and securing the freedom of Israel from him. God says that Moses should first go to the elders of Israel and those elders would support Moses’ mission. This never happens; the elders reject Moses. Neither do the elders go to pharaoh to ask for release.
Moses himself does not see this statement by God as a prediction of the future (or clairvoyance of future acts). Instead, Moses begins questioning God, skeptical that the elders will listen to him. God responds by giving Moses a series of miracles by which he can convince Israel. Ultimately, none of these work, and Moses receives only resistance from the elders of Israel while he tries to liberate Israel.
God is predicting actions, not foreseeing events. Those actions are free and do not turn out as predicted. Neither Moses nor God treat the future as set and foreknown. Instead, they see God’s predictions as not concrete and not necessarily accurate. God never responds to Moses’ skepticism with an account of divine foreknowledge. God responds with a cascading contingency plan in case the people are not convinced. God treats the future as no settled, and His own predictions as possible scenarios.’
source: Christopher Fisher, “Exodus 3:18 Commentary” (godisopen).