The novel ends with John and Gabriel staring at each other in the doorway of their house after John's conversion, with Elizabeth waiting inside. The final lines are John's words:
"I'm ready," John said, "I'm coming. I'm on my way." (3.1.282)
So what does this mean? Who is he talking to? What's he ready for, exactly?
The ending is ambiguous. We've got guesses for all of these questions, but they're just that: guesses. He could be literally just telling his mother that he's on his way into the house, so it appears as if these lines are directed toward Gabriel. After all, he's facing Gabriel, not her.
So is he telling Gabriel to watch out? Perhaps John is saying that, now that he's saved, he's ready to confront his bullying father; that he's coming for him.
Or, in a more optimistic light, John could be saying that he's coming up: he's ascending to the top. He's becoming more spiritual, a better person, a grown man.
It's hard to narrow down the meaning with this one. But hey, when you're reading a work by someone as literarily significant and brilliant as James Baldwin, you don't have to choose just one meaning. You can have your cake and eat it too; you can be a greedypants and accept all these meanings as existent and valuable. Everybody (except hopefully Gabriel, that jerko) wins.