The Egyptian economy depended on a huge slave resource. There were probably millions who toiled in bondage with little hope of ever breaking free. Presumably many tried to escape, but to little avail.
No wonder that their imagination was stirred when the Hebrew slaves seemed set to succeed. No wonder that when the Exodus finally happened, there were hangers-on who tried to merge with the bid for freedom
The Bible calls them a mixed multitude, an erev rav – literally, as Rashbam points out, “a great mixture” (Ex. 12:38).
The erev rav presumably asked no questions as to whether they fitted into Hebrew society. It was enough to be on the way to escape.
Did the Hebrew slaves resent the presence of the hangers-on?
The Midrash is bothered by the question and indicates that the Almighty was not too pleased to have an erev rav. When God commanded the Israelites to slaughter a lamb and place its blood on their doorposts “as a sign to you” (Ex. 12:13), the words “to you” restricts the sign to the Israelites (Rashi). Hence, say the sages, the blood was placed inside the doorposts.
It is not that the erev rav were not suffering human beings who also deserved a place in the sun, but the fear was that their presence would affect the spiritual commitment and nation-building of the Israelites.