Shemot Rabbah

It has been said ‘It is easier to take the Jew out of the Exile, than to take the Exile out of the Jew’. While in Egypt, the Jewish people could not even hear Hashem’s promise of Redemption because of their “shortness of spirit.” Their bondage wasn’t merely a physical bondage, but a mental one. And so, while still in Egypt, Hashem began the process of taking the Jew out of the psychology of Exile, ridding him of his slave mentality.