Well, at least Our Lady did come from the lineage of Abraham and Sarah through Isaac and then Jacob.

But with respect to Sarah's knowledge of Abraham's sacrifice, we couldn't be too sure. On my part, I just imagine that Sarah, with maternal instinct sensed 'something was up' that day when Abraham and Isaac left for Moriah. And I could just imagine her praying hard and putting her trust in God, just as Abraham did.

“By faith Sarah herself received power to conceive, even when she was past the age, since she considered him faithful who had promised.” (Heb 11:11) We can somehow relate this to Mary, not because Mary was already too old to conceive like in Sarah's case, but that Mary chose to maintain her virginity. But even in different circumstances both Sarah and Mary "considered him (God) faithful who had promised."

And as Elizabeth told Mary, “blessed is she who believed that there would be a fulfillment of what was spoken to her from the Lord.” (Luke 1:45)

At least this aspect of humanity is not a mystery, but genetics (has a lot to do with melanin). Difference in skin color (or any other external appearance) does not mean difference in humanity; even two human beings who look very different are in fact genetically very close to each other. So changes in external appearance already depend on where the descendants of Adam and Eve would would encounter themselves later on. (we don't even know Adam and Eve's skin color; but whatever it was, all of us belong nevertheless to the one human race; as the Wiki page on the Human Genome Project says: "The utility of the project comes from the fact that the vast majority of the human genome is the same in all humans")

Regarding what science could say regarding human skin color, perhaps these articles could provide some further insight:

Human subspecies or races? | Ask A Biologist (asu.edu)

Modern Human Diversity - Skin Color | The Smithsonian Institution's Human Origins Program

Modern Human Diversity - Genetics | The Smithsonian Institution's Human Origins Program

The Bible is not 'anti-Ishmael'. Hagar and Ishmael being banished from Abraham's household should be taken in its proper context: Sarah was quite affected by how Hagar, Ishmael's mother, treated her when Ishmael was born (cf. Gen 16:1-5); what ensued afterwards was more of handling this feud between Sarah and her maidservant, and not because of a negative outlook on Ishmael.

Being nevertheless Abraham's son, God also greatly blessed Ishmael (cf. Gen 16:9-13; 21:11-21). And though the fulfillment of the promise of universal blessing will course *through* Isaac (it's not even Isaac himself), it's because God chose it to be so, and not for any merit on Isaac's part; and that's no reason for anyone to feel envy or inferiority for it, especially because the promised blessing goes out to all of humanity anyway.

Both Isaac and Ishmael were together to pay their final respects to their departed father (Gen 25:8-9). That there was bitterness between Sarah and Hagar doesn't mean that there was also conflict between Isaac and Ishmael. The Bible never mentions enmity between the two half-brothers, both honored sons of Abraham.

It would also be important to note that the protagonists of the New Testament (John the Baptist, Elizabeth and Zachary; Jesus, Mary and Joseph; the apostles, St. Paul, and the first Christians) all came from the Jewish people.

God would know what to do. St. Paul also thought and prayed hard about this, and I invite you to read Romans 9-11 to see what he thinks about it.

It's not as if Abraham was somehow "externally controlled" to do something that he didn't want to. That wouldn't have been meritorious on his part, and that would have been a caricature of the act of faith. When he obeyed it was because of his deep faith and trust in God, who was accompanying him and helping him all throughout. We could imagine that he also had to sort this out with a lot of intense prayer, similar to Jesus in Gethsemane.

“By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only son, of whom it was said, “Through Isaac shall your offspring be named.” He considered that God was able even to raise him from the dead, from which, figuratively speaking, he did receive him back.” (Heb 11:17–19)

So this teaches us that he really considered things deeply, and didn't just 'jump up and act blindly'.

Scott in his book also wanted to highlight this fact in Gen 22:5 “Then Abraham said to his young men, 'Stay here with the donkey; I and the boy will go over there and worship and come back to you.'” In the original Hebrew the verb 'go over' and 'come back' are both in *first person plural*: in a way showing how Abraham firmly trusted God in that *both he and his son*, the son of the promise, would somehow be back safe and sound (giving us a background to Heb 11:17-19).

“For circumcision indeed is of value if you obey the law, but if you break the law, your circumcision becomes uncircumcision. So, if a man who is uncircumcised keeps the precepts of the law, will not his uncircumcision be regarded as circumcision? Then he who is physically uncircumcised but keeps the law will condemn you who have the written code and circumcision but break the law. For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.” (Rom 2:25–29)

“Is this blessing then only for the circumcised, or also for the uncircumcised? For we say that faith was counted to Abraham as righteousness. How then was it counted to him? Was it before or after he had been circumcised? It was not after, but before he was circumcised. He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the father of all who believe without being circumcised, so that righteousness would be counted to them as well, and to make him the father of the circumcised who are not merely circumcised but who also walk in the footsteps of the faith that our father Abraham had before he was circumcised.” (Rom 4:9–12)