Genesis 1-11 is about how the world became such a mess. Genesis 12 begins the story (which is still unfolding) of what God is doing to fix the mess. God’s plan is laughable: he will save the world through one man’s family. That man is Abram (later called Abraham).
There is a problem, however: “Abraham and Sarah [his wife] were old, advanced in years, and “the way of women had ceased to be with Sarah.” In Genesis 15, we read how God made a covenant with Abram and promised Abram as many children as there are stars in the sky, and that through that family would God bless the whole world. So the fact that Abraham and Sarah still do not have children is a major problem.
In Genesis 15, Sarah takes matters into her own hands and decides to have Abraham father a child through her servant. He does, and unsurprisingly the servants pregnancy causes problems in the family. Whenever we decide to use our means to achieve God’s ends, it always goes badly for us.
16:6, One of the original sins of men is passivity. That was Adam’s sin at the Fall–“It was the woman YOU gave me, Lord”–and that’s Abram’s sin here (along with the obvious sin of lust.” He agrees to do what he knows is wrong by sleeping with the maid, and then he refuses to speak up for her. I think this verse is heartbreaking.
16:11-14, Circumcision is like a gang tattoo: it’s meant to signify your allegiance. Think of the significance, then, that baby boys are circumcised before they know what it signifies. What this means is that God’s covenant comes to us first, before we deserve it or earn it. It is a covenant of grace.
16:18-19, Abraham wants God to make the covenant with his son Ishmael, the first-born. But, as we’ll see over and over again with the patriarchs, God subverts primogeniture and chooses the younger son. God has a way of subverting human expectations.
17:17 – Abraham thinks God’s plan is ridiculous. And he’s right. But, God works in ridiculous ways.
18:1-8 – Note the picture of ancient Near Eastern hospitality: Abraham drops what he’s doing to care for his guests.
18:1 – It’s a very mysterious guest that Abraham entertains, but though we know it is a divine guest, Abraham does not. (The event is referenced in Hebrews 13:2: “Do not forget to show hospitality to strangers, for by so doing some people have shown hospitality to angels without knowing it.”)