(2) A covenant is like a contract but seems to be deeper than a mere contract in terms of the amount of emphasis on the weight of the promises made. This is shown by the number of assurances God makes in each covenant, and is also true if you consider the common theological understanding of the history of the Jewish people as one in which God kept the covenant even when they did not. Genesis 9:8-17 is different than Genesis 15 or Genesis 17 in that it is a covenant between God and all living beings not between God and a specific individual or group. However, Genesis 9:8-17 is more similar to Genesis 17 than to Genesis 15 because both seem to be instances of God directly speaking, rather than mediated through a dreamlike state, both have God use the word “covenant” extensively, and both are marked by a sign (a rainbow and circumcision). The reason for this may be that there were two accounts of the story of God making the covenant with Abraham, one of which was modeled after the covenant with Noah and the other was independent. These two versions may have both been included.
(3) In one respect the amount of movement in and out of the Promised Land may be meant to speak to Jews who themselves were made to travel from their homeland and were dispersed. While Abraham’s family did the same ultimately they came back to their rightful place. This may be a manner in which the Biblical authors and editors meant to reassure the Jewish people that they would be returned to their rightful place as well.
In the same vein a lot of the travel may be part of solidifying Israel’s claim to the land. By mentioning things that they pass (for example Bethel) the text sets a precedent for claims to lands which everyone would have been familiar with. Additionally, Abraham’s family doesn’t intermarry with the Canaanites. There are probably two related reasons why this is pointed out. The first would be to establish that the Canaanites are not the rightful owners of the land by clarifying that they have no common ancestry with the descendants of Abraham and therefore cannot be coheirs to the covenant. The second has to do with how in Genesis 9:27 the Canaanites are cursed with slavery because of the actions of Ham. Since the Canaanites are cursed and meant to be slaves it should be clear that the Jewish people are distinct from them. Finally, in Genesis 15:13-16 it is established that Abraham’s descendants must leave the Promised Land and serve another nation. So when Israel leaves Canaan for Egypt it is clear that this is something which must happen but which is only temporary.