I don't think this is a book about a lullaby! (Although that's "All the Pretty LITTLE Horses".) But in the end, it is all that John Grady Cole can rely upon, so it is relevant in that respect.
McCarthy's books are distinctive for how they make you feel as you read them. This one is no different from any other I've read by him. He sets the stage through his style of writing - compact, reflective, evocative of another time and place - and lets you recognize what works for you and ignore what doesn't. The most useful thing I can say about McCarthy's writing is that he creates utterly believable characters in so few strokes of the pen. John and Rawlins, sure, but also Blevins and the captain and Alejandra herself. And that amazing Mexican countryside, which is clearly a character in and of itself. (I'd go visit if those "men of the country" weren't even more terrifying nowadays.)
I know this is a trilogy. But I'm not ready for the next parts of what McCarthy wants to tell me because I'm not ready for John to to move on from the results of this tale. He knows, you know, and I know that he has to sit with these feelings for some time before moving onwards. (OK, that's weird when it's a fictional character, but that's how strongly this affected me.)