[See Likutei Sichos vol. 16 pp. 475-479]. This oral class (based on a Sicha, though no Sicha was read), explains that for a nation to be born, where even the greatest sinners are members, we must be branded on the deepest levels of the subconscious, and that was Galus Mitzrayim. We are not a free nation until the nationhood shows itself in the physical world, thus we are not free until Hashem has a home on earth- the Mishkan. Thus every word from the beginning of Shmos until the end is all about one thing: Exodus.