Right. If you combine this book and this sheet of paper, using a code that does not get written down, but should be simple enough to memorize, you get ten different guesses by Keltham at a wish phrasing that could destroy Cheliax. They have adjustable parameters depending on how large a crater you want to create.
The sensible thing to do here, and what Cheliax should expect Keltham to do if they're modeling him almost correctly, would be to pull in a high-circle wizard trusted of Iomedae, who knew what there was to be known about Wish phrasings, and have him work with Keltham on adjusting these.
Keltham cannot do this because he is in the middle of an absurdly complicated situation that he has not in fact decrypted, he has suspicions he's not trying to think about too hard, and he was told in a vision from Iomedae that Cayden Cailean might possibly have had good reasons for destroying Iomedae's intelligence apparatus in Cheliax which implies that they might be dealing with information hazardous to Iomedae Herself.
Keltham's current plan is that he's going to have to find out what's usually known about Wish phrasings on his own without any help from Iomedan or Abadaran forces. Afterwards he may hand over an improved set of Wish phrasings for destroying things. Until then, they're going to need to take the information here and work out on their own how to adjust the phrasing, if it comes to that. All this is to be understood as an emergency measure intended to prevent Cheliax from definitely winning immediately if somebody takes out Keltham permanently, and to make that Chelish victory be not a thing that is knowable to somebody predicting Keltham.
In the event that Keltham gets removed from the gameboard, they should possibly consider trying to spring an ambush on Asmodeus, Urgathoa, or whichever other god is being most inconvenient to Iomedae's plans, using a suggested design he included for conjuring matter in a container that will explode if magic is removed from it, which you could maybe drop onto the ninth plane of Hell and create an explosion large enough to destroy whatever chunk of Asmodeus usually lives there. A few rounds before they destroy Cheliax, would be the plan there, ideally; you can lose the advantage of surprise to a god in a few rounds, if you destroy Cheliax first, but an assault on Asmodeus shouldn't alert Cheliax the same way.
Keltham also needs to write a testament giving over his Project Lawful shares to somebody not in Cheliax, if Keltham permadies. The pharaoh of Osirion is an obvious choice but Keltham is open to hearing how an Iomedan would be a better choice. Keltham is pretty sure that he is more aligned with Iomedae than Abadar; he's nowhere near as sure about the Pharaoh of Osirion versus the Queen of Mendev.