Commentary for Genesis 12:8

ויעתק משם AND HE REMOVED FROM THERE — supply the word אהלו “his tent”.

AND HE CALLED UPON THE NAME OF THE ETERNAL. Onkelos explained it as meaning that he prayed there, just as in the verse, I called upon Thy name, O Eternal, out of the lowest dungeon.⁶¹Lamentations 3:55.
The correct interpretation is that Abraham loudly proclaimed the name of the Eternal there before the altar, informing people of Him and of His Divine essence. In Ur of the Chaldees he taught people but they refused to listen. Now, however, that he had come to the land concerning which he had been promised, And I will bless them that bless thee,⁶²Verse 3 here. he became accustomed to teach and to proclaim the Deity. Scripture likewise tells of Isaac — when he went to the valley of Gerar where he was promised, Fear not, for I am with thee⁶³Further, 26:24. — that he built an altar there and invoked the name of the Eternal⁶⁴Ibid., Verse 25. since he had come to a new place where they had not heard of His fame or seen His glory, and he proclaimed His glory among these nations.⁶⁵See Isaiah 66:19. Now a similar statement is not made concerning Jacob, [i.e., that he proclaimed the name of the Eternal before the peoples of the land of Canaan], for since he begot many children — all of whom were worshippers of G-d — and he had a great community, which was called “the congregation of Israel,”⁶⁶Exodus 12:3, et al. it was through them that the Faith was proclaimed and became known to all people. Besides, the Faith had been proclaimed throughout the entire land of Canaan since the days of his ancestors. In Bereshith Rabbah⁶⁷39:24. the Rabbis similarly say, “And he called upon the name of the Eternal. This teaches us that he caused the name of the Holy One, blessed be He, to be in the mouth of all people.”

בית אל מים והעי מקדם, between two large cities, in order to attract large crowds who could hear him preach.