"Slaves were we to Pharaoh in Egypt". Question – (It would have sufficed to) mention one of them, either Pharaoh or Egypt. This is meant to relate how great the miracle of the redemption was. When a person is enslaved to a single master, the latter might have compassion and release the slave, or do so when approaching death or after dying, which is when slaves can, as a rule, be released. However, when one is enslaved to many people it becomes difficult for them to all agree to release the slave, and leaves little hope of redemption. This was the situation of the People of Israel, who had little hope of redemption resulting from their dominator's choice