C. F. Keil and Franz Delitzsch on Exodus 12:38-39

Exo 12:38-39

In typical fulfilment of the promise in Gen 12:3, and no doubt induced by the signs and wonders of the Lord in Egypt to seek their good among the Israelites, a great crowd of mixed people (רב ערב) attached themselves to them, whom Israel could not shake off, although they afterwards became a snare to them (Num 11:4). ערב: lit., a mixture, ἐπίμικτος sc., λαός (lxx), a swarm of foreigners; called אספסף in Num 11:4, a medley, or crowd of people of different nations. According to Deu 29:10, they seem to have occupied a very low position among the Israelites, and to have furnished the nation of God with hewers of wood and drawers of water. - On Exo 12:29, see Exo 12:34.