First thing that's mentioned is Abraham's "other" children. I frequently get the sense that almost nobody knows about this "other" wife, Keturah, and his "other" sons. This is because so much emphasis is placed on Isaac and Ishmael, both later in the bible and in further discussion and sermonizing. This is perhaps rightly, as these two figures are certainly the most important of Abraham's children, both for theological and historical reasons.
It almost seems like a "life goes on" moment for Abraham, in that he remarries after Sarah dies, and then has some more children like he were a normal person (in spite of his great age and long barrenness before conceiving Ishmael). But at the same time, he still obviously favors Isaac over all, by expelling his younger children from the promised land, which he reserves for Isaac. Then Abraham dies and is buried in his familial crypt with Sarah.
Also, note that some of Abraham's "other" children go on to become great nations. Midian contends with Israel frequently, Sheba and Dedan are forefathers of large countries, the Asshurites being a primitive reference to the Assyrians.
None of the children of Ishmael are particularly notable from what I know. It's funny how this chapter says they settled "in defiance" of their relatives, continuing the antagonism between Isaac and Ishmael. Sufficed to say, nobody likes getting surpassed by their younger sibling.
One of my favorite passages is right here, where it says that Isaac prayed for his wife to conceive, because she was barren. This is a very bright note in the midst of some really bitter stories before and after, amongst the trio of Abraham/Isaac/Jacob.
Abraham and Sarah were barren, so Abraham resorts to sleeping with her handmaiden, Hagar. This results in the contention between Ishmael and Isaac, which continues for generations. Jacob and his favored wife, Rachel, have trouble conceiving and in short, this results in lots of contention in their family too, as Jacob sleeps with Rachel's handmaiden, Bilhah (this happens later in Genesis, so I will not discuss it further here; more detail will be provided when we reach that section).
From a literary-analytical point of view, many people would say these are repetitions of the same story. However, from a more direct historical/theological point of view, it's pretty clear that barrenness runs in Abraham's family. There are a couple different explanations for this. One is the literary repetition, like I mentioned. Next is the possibility of some genetic condition that causes barrenness being passed down. Edit: A generous commenter pointed out that since the barrenness was on the female side, it couldn't have been passed down through Abraham, so strictly speaking it doesn't "run in Abraham's family" in a genetic sense. However, Sarah, Rebekah and Rachel (who we meet later) are all genetically related on their side of the family through Nahor, and they are all descended from Terah, the father of Abraham. So a genetic cause is plausible /End Edit. And lastly, there is the possibility of some spiritual condition or curse of some kind that is attacking his family. This last explanation is somewhat common in conservative circles, as commentators note that Satan would have a pretty clear incentive to cut off the nation of Israel before it can become a carrier for the Messiah. In my opinion, it's likely there is some sort of spiritual condition here, but I'm not sure it can be directly ascribed to demonic forces as we have yet to see any sign that the demonic forces are aware of Abraham's promises of greatness or what they ultimately entail for humanity.
One way or another, there is a clear history (and future) of barrenness amongst this trio of patriarchs, and the only one whose response is godly is Isaac. Both Abraham and Jacob look for human solutions, but instead of taking on a concubine and disrespecting Rebekah, Isaac turns to God and prayer, and as a result Rebekah is able to bear children without having to suffer the same ignominy as the other two women put in her position. Thus, Isaac clearly has the most tranquil domestic life of the three patriarchs.
Unfortunately, in spite of Isaac's good response, his two children are at war from birth. This continues the two main trends we saw with Ishmael and Isaac: the younger is heir of the promises, and both children are at war with each other.
The "elder serving the younger" seems to be one of the central themes of the bible, and I think it's closely related to other NT concepts like God overthrowing the "wisdom of the wise". It is a strongly established cultural principle (at the time) that the eldest was heir to the birthright and a double portion. Even in Israelite law, the eldest was assured a double portion of the inheritance, which is ironic because Jacob himself, who is later renamed Israel, steals the double portion of blessing from his elder brother. This shows both the controversy of Israel's establishment as the forefather of the Jewish nation, and also the way that God overturns human principle when he desires. Oftentimes, we won't like it, but he is God and he does as he pleases.
Certainly Ishmael didn't like it, and Esau will not like it either, as we will see in detail. An added dimension to this is that God only speaks to Rebekah about Jacob's elevated status. Importantly, this information is not shared with Jacob, Esau or Isaac. So we will see Rebekah secretly support Jacob, while Isaac supports Esau.
Less significantly, note that "grasping the heel" is a Hebrew expression that more or less means "trying to pull this guy down so that I can step over him and take his place". Jacob, as a name, means something along the lines of "deceiver". So already at birth, one might question God's wisdom in choosing this deceiver, this supplanter of his elder's right, as the chosen son whom the elder shall serve.
At the same time, Esau deliberately and willingly trades his birthright to Jacob for a pot of stew and some bread. So, as the bible notes, Esau "despised his birthright". One might ask, what is a birthright? To the best of my knowledge, this is his preference as the eldest to a double portion of inheritance from their father. What's strange about this story is that to the best of my knowledge, neither the birthright or the inheritance is ever actually mentioned as being distributed in the bible. Esau will mention it once later on, but it's never actually described how much of Isaac's fortune is given to his two sons. Presumably this is because the actual distribution of money isn't important. That's why, in my opinion, the more significant element is the spiritual or authoritative position as the firstborn, which Esau also gives away to Jacob. This is indeed the more significant element of what God spoke to Rebekah, but Jacob isn't done attaining it. We will see another element of Jacob's deception later in this book.