The God of this people Israel selected our forefathers and made this people great and important during their stay in the land of Egypt, and then with an uplifted arm He led them out from there. [Exod. 6:1, 6.]
And this is [in effect] what God told him: That his descendants would be aliens (strangers) in a land belonging to other people, who would bring them into bondage and ill-treat them 400 years.