Abarbanel offers three reasons why Avram had to leave Haran. First of all, the region was full of heretics who did not recognize G-d's existence. Secondly, these idolaters — who were his friends, neighbors and relatives — were opposed to his “proselytizing”. They saw what had happened to him in Ur Kasdim, where he was miraculously saved from a fiery furnace, and forbade him from continuing his teaching. Thirdly, Avram was reluctant to correct the behavior of his father and brother who were manufacturers of idols. G-d does not tell him explicitly where to go, in order to prevent his family from following him.
Realizing that such a drastic move would be difficult for Avram, G-d assures him that he will make him “a great nation” — meaning he will have offspring who will be dearer to him than his father and brother, upon whom he had always relied. Secondly, to replace the friends and associates who had helped him to prosper, G-d assures him that “I will bless you and make your name great.” G-d is the ultimate source of all prosperity. G-d also assures him that “I will bless those who bless you, and he who curses you I will curse”. “Those who bless you” is in the plural, indicating that they will be far more numerous than those who curse. Finally, not only will Avram benefit from the new land, but those who accept his teachings will benefit as well — "and all the families of the land will be blessed through you."
How then does Avram know where to go? Abarbanel offers five reasons:
- Avram knew that Canaan had been the ultimate destination of the family when they had left Ur Kasdim.
- Avram knew that the very air of Canaan imparted wisdom.
- Avram knew that Canaan was in the portion bequeathed to Shem, the most righteous of Noach's sons and that part of it was ruled by Malcheitzedik, a man committed to monotheism.
- Avram knew that Canaan was under G-d's direct Divine Providence.
- Given that there was a tradition that Adam was buried there it makes sense that Avram would be drawn to that area.