Musar על בבא קמא 75:2

The theme of the linkage between the sanctity of the land of Israel and the giving of the land of Israel to Abraham and his descendants is repeated no less than three times in this portion of the Torah. At the beginning of the פרשה Abraham is invited to move to the land of Canaan and to traverse it. Once he had done so G–d promises the land to Abraham's descendants in 12,7, without specifying any boundaries. We find the specification of the boundaries spelled out in the middle of the פרשה in 15,18: "On that day G–d concluded a covenant with Abraham saying: to your descendants I have given this land from the river of Egypt up unto the great river, the river Euphrates." The promise is reiterated a third time near the end of the פרשה in 17,8 where G–d says: "I have given to you and to your descendants after you the land in which you sojourn, the whole of the land of Canaan as an everlasting inheritance, and I shall be their G–d." Each of the three promises represents an "improvement," something additional.