Charlie isn't omniscient. If I were Parson, I would be thinking:
1) Charlie REALLY wants him to use that scroll, for some reason. Why not just let him die in the fire? So there must be some upside to Charlie if Parson uses it, perhaps turning Parson into Charlie's puppet.
2) The caster angle is interesting. As a previous poster indicated, it would be good to start using calculations to figure out what he might be capable of. Meanwhile, he could parallel track the following plan...
3) Order the remaining red dwagons to converge on the remaining soldiers, and have the soldiers all harvest the red dwagons, and then go fight the worst parts of the inferno.
4) As the units start croaking, the Tool starts receiving natural thinkamancy updates that show how dire the situation is, with only Parson remaining. Maybe that would goad him into changing the capital as Parson requested.
5) If not, Parson could still try the start a new side gambit. If that works, he walks out to the MK and learns how to use his magic.
6) If the new side gambit doesn't work (perhaps the summoning spell won't let him), then he either chooses to read the scroll or die in the fire.
7) The above is a layered set of contingencies, one of which might actually work. But at the end of the day, I'm betting Parson does something completely different.