The LORD appears at Mamre as three men; Abraham shows them lavish hospitality, and Hebrews thirteen will later draw the general principle from scenes like this one — "some have entertained angels unawares." Sarah, listening at the tent flap, laughs privately at the promise of a son within the year, and gets asked the question that stands over the whole cycle: "Is any thing too hard for the LORD?"
Then something remarkable happens — God deliberates out loud, disclosing His plan to judge Sodom, specifically because of who Abraham is meant to become: someone who will "command his children and his household after him... to do justice and judgment." And Abraham does the thing that earns him a title used nowhere else in Scripture for anyone else quite this way — he argues God down, from fifty righteous to ten, on the ground of God's own justice: "Shall not the Judge of all the earth do right?" That title comes a few verses later than this scene, in James 2:23 — "the Friend of God" — but it's rooted in exactly this kind of intimacy, and it isn't unique to James. Isaiah forty-one and 2 Chronicles twenty both independently land on the same title, centuries apart, which tells you it had become a settled description, not a one-off compliment. This is, not coincidentally, the title John Lennox's own book on Abraham takes its name from — he reads this relationship of genuine, reciprocal disclosure as the theological center of gravity for the whole story, more than the covenant mechanics or even the Akedah.