There will be false redeemers. Joseph knows this. Before he closes his eyes, he hands his children a test.
The Targum Pseudo-Jonathan on Genesis (50:25) expands his oath dramatically. Joseph does not simply ask that his bones be carried out. He swears his brothers' sons to warn their sons: "Behold, you will be brought into servitude in Mizraim. But you shall not presume to go up out of Mizraim until the time that two Deliverers shall come, and say to you, Remembering, remember ye the Lord."
Two deliverers. That is the Targum's expansion — and it points forward to Moses and Aaron, who will arrive centuries later and speak the exact phrase Joseph plants here. The doubled verb is the sign. The man who appears with power but without the password is not the one.
This is a brilliant piece of ancient counter-intelligence. Joseph cannot predict when redemption will come. He cannot predict what form it will take. But he can hand down a passphrase, and he can make every generation rehearse it until the right voice speaks it back.
"At the time when ye go up," Joseph adds, "ye shall carry up my bones from hence."
The Targum's Joseph is teaching Israel two survival tools at once. A password, so they will recognize the real redemption. And a burden — a coffin — so they will never grow too comfortable to leave. Both tools worked. Moses carried the bones. Israel carried the phrase. The Maggid closes his eyes: faith is the refusal to forget the password.