Why did Israel need to be in their own land rather than remain slaves in Egypt?
Because God's covenant with Abraham required not only a numerous people but a distinct geographical homeland. As a nation through whom God would work, Israel could not remain enslaved in Egypt; they had to occupy their own borders and land, as promised in the Abrahamic covenant.
Les teaches that the Abrahamic covenant included both a people and a place. God promised Abraham, “I will make of thee a great nation,” and Israel did become a large people—anywhere from 3 to 7 million, about 5 million in antiquity. But God also had to put them in a geographical area of land. They could not just continue on in slavery in Egypt. If they were going to be a nation of people that God would work through, they had to be in their own borders. The earlier context also shows God called Abraham to separate from false religions, because one cannot serve God while under the roof with idolaters.