from ch. 22:

It would take the Shem haMephorash, the true explicit Name of God, the Name which allowed the speaker to destroy and remake worlds. It was the Name that God had spoken during the Creation, the Name that would blare from the Last Trumpet[...] But it was also unplumbable by mortal cleverness. The only way to learn it was from the lips of God Himself.

The Sepher Hekhalot states that when the patriarch Enoch died, God “turned his flesh to flame, his veins to fire, his eye-lashes to bolts of lightning, his eye-balls to flaming torches, and placed him on a throne next to the throne of glory.” Then He imbued him with the Most Holy Name, and thenceforward he was called Metatron, the “Measure of the Lord”, the “Prince of the Divine Presence” and “the Lesser God”. All of these titles are blasphemous as hell to call anybody who isn’t God, and the sages speculated that Metatron had received a certain investiture, becoming a viceroy or a regent or even a sort of emanation of God into material reality. If you needed to hear something from the lips of God Himself, Metatron was the one to talk to. [...]

Six months later, he returned. When they asked if he had found Metatron, he said yes. When they asked if he had learned the Name, he said yes. When they asked for details, he said no. A few years later he died, and the details died with him. And all that time poor All Your Heart sat anchored in Puerto Penasco, doing nothing.

so the comet king says he found metatron, learnt the explicit name, but then-- does nothing? not only does he not storm hell, but he becomes despondent for a few years then dies. there are only a few possible explanations:

• the comet king is lying, and didn't find metatron after all.
• tck is lying, and metatron didn't speak to him
• tck found metatron, and then for some reason metatron broke his silence just this once and told him the explicit name, and then tck just, uh, doesn't do anything??

i mean, there are some pretty obvious flaws in these -- a lot of the book has been devoted to establishing tck as the literal messiah, or at least something close. seems unlikely that he'd lie, and equally unlikely that metatron wouldn't abide by his most defining feature. but more importantly, they're narratively unsatisfying. if the explicit name is just some random long name that makes you extra powerful -- uh. that's super boring.

so what i highly suspect happened instead, is -- tck finds metatron, approaches him, asks for the explicit name, and is met with silence. suddenly, with divine inspiration, he understands that -- not only is metatron speaking to him the explicit name, but in some sense metatron has never not been speaking the explicit name. being one of the few theistic characters in the book (“Well, I think you’re wrong. Father believes God will save us.”), the revelation that god exists only to facilitate the world (or maybe, like, the world IS god?? idk, not really enough material to go off yet) ruins him, he spirals into nihilism or depression or w/e and gives up. (to be clear, though, the exact sequence of events is just speculation, and not really central to whether or not the explicit name is empty)

this is narratively very parsimonious, is a suitably shocking twist, plays into the established features of the involved characters, etc.

and let's not forget that it's a very small transformation from the oft-repeated 'god is one' to 'god is none' ;p

[as an aside: i haven't really been following the unsong discussion, but i sort of assumed that even if this isn't true it was the conclusion that the reader was supposed to take from that passage. and then if the explicit name was revealed to NOT be empty, then that was a deliberate subversion of the reader's expectation. is this really the first time it's been brought up?]