If you think about it, David, God began limiting his revelation long before Abraham.
In Genesis, we read that Seth was appointed the next "offspring" in place of Abel (Gen. 4:25). After this, Seth had a son and "at that time people began to call upon the name of the Lord" (Gen. 4:26). We see here a distinction between Cain's degenerating posterity (Gen. 4:23-24) from Seth's.
Remember the prophecy. "I will put enmity between you and the woman, and between your offspring and her
offspring; he shall bruise your head, and you shall bruise his heel” (Gen. 3:15).
In the next chapter, we read a long chronogeneaology of Seth's line until we reach righteous Noah. "The Lord saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually" (Gen. 6:5), all except Noah, who "was a righteous man, blameless in his generation. [He] walked with God" (Gen. 6:9). It was through him and his family that God spared mankind from utter destruction.
Remember the prophecy. "I will put enmity between you and the woman, and between your offspring and her
offspring; he shall bruise your head, and you shall bruise his heel” (Gen. 3:15).
After the flood, Noah makes this public declaration about his son Shem: "Blessed be the Lord, the God of Shem; and let Canaan be his servant. May God enlarge Japheth, and let him dwell in the tents of Shem, and let Canaan be his servant" (Gen. 9:26). Here he states that the Lord is the God of Shem (similar to the saying that Jehovah is personally the "God of Israel"). He also makes a messianic reference of Jepheth dwelling in the tents of Shem, whom God is personally known in and acquainted with in the aforementioned statement.
Remember the prophecy. "I will put enmity between you and the woman, and between your offspring and her
offspring; he shall bruise your head, and you shall bruise his heel” (Gen. 3:15).
God has now distinguished Shem's descendants from the rest of mankind until we reach the Tower of Babel, when the rest of mankind rebel against the authority of God. In the record of the chronogenealogies, among the descendants of Shem, we find that there was a man named 'Eber' who had a son named Peleg (Heb. "divided") on account that "in his days the earth was divided." It is theorized that this individual marked the generation that these events occurred.
There is something significant with Eber, his father, as well. Before we read any names from this pedigree, the inspired author says this - "To Shem also,
the father of all the children of Eber" (Gen. 10:21). Why was he mentioned in this fashion? He is three generations away from Noah, is he a significant figure in the history of the Hebrew people? It is argued that the name 'Hebrew' is originates the name 'Eber' (also called 'Heber'), and that a Hebrew was one who was descended from the man 'Eber.' If this is true, then the Hebrew "race" was separated at Babel from the rest of Shem, Ham, and Jepheth's children. It was through Heber, and that through Peleg, Genesis 3:15 must proceed to be fulfilled.
Then we reach Abraham, who had Ishmael and Isaac, and that "through Isaac shall your
offspring be named" (Gen. 21:12). Isaac had Esau and Jacob (Israel).
God was narrowing his revelation from time to time, until at last...
I'll let you or others figure out why God limited himself only to Israel...
