A lot happens to Abram before we get to chapter 17, but most of it seems to fit together without making false cosmological claims or implying ridiculous divine behavior. In this chapter God makes his covenant with Abram/Abraham, which requires a little sacrifice (circumcision) from Abraham, his descendants, and his slaves. To be fair to Abraham, he is 99 years old at this point and no doubt is less concerned about the condition of his member than, say, 13-year-old Ishmael. We’re not told how the new ritual is received beyond that it just is.
I’ll leave, to other blogs and commentators, the controversy of mutilating the genitals of someone who is not old enough (Gen. 17:12) or free enough (Gen. 17:13) to consent . I’m more interested in why God would choose this method for distinguishing his people and also what compels him to have his own people at all.
I understand the purpose of circumcision as an irreversible physical sign of the covenant that distinguishes Abraham’s nation from the surrounding pagans/Gentiles. In the context of the first sixteen chapters of Genesis, however, I would expect the shame of nakedness that Adam (Gen. 3:10) and Noah (Gen. 9:21-27) feel would make circumcision less than ideal as a way to identify someone in your tribe. Are we to believe that the Hebrews went around exposing themselves to each other to prove their commitment (Gen. 17:14)? Assuming they maintained their modesty this might be impractical to enforce.
There are better physical modifications that would serve the purpose of an irreversible identifier of the tribe. For example, a particular tattoo or burn would work, cropping one or both ears, removing the eyebrows, forking the tongue, etc. etc. etc. All of these could serve the purpose just as well as a circumcised penis and they’re not gender specific, so the women could even participate in the covenant.
The most troubling lesson from this story is that God deliberately chooses one group of people for his revelations and protection. That hardly seems fair to the rest of humanity, especially considering God is the one responsible for dispersing them and setting up rivalries in the first place. God is less concerned about the well being of his creation and more concerned about winning, whatever that may mean.