家法甚嚴 The Rules Here Are Strict
我那大王家法甚嚴，燒火的只管燒火，巡山的只管巡山。終不然教你燒火，又教你來巡山？」我那大王家法甚严，烧火的只管烧火，巡山的只管巡山。终不然教你烧火，又教你来巡山？」
逐句解 Line by line
"The rules in my king's house are very strict. Firelighters do nothing but light fires and mountain patrols do nothing but patrol the mountain.
家法甚嚴 is house discipline, strict — 甚 here as shèn, very, against the shén it takes inside the two-character question word. 只管 doubled across the two clauses is the whole objection: each post does its own work and nothing else.
It is not to be thought of that they would set you to light fires and then send you to patrol the mountain as well."
終不然 is a strong rhetorical after all, surely not. And 教 twice is jiào, the causative — make you, set you to. The little demon has found the flaw in the cover story, and it is a personnel flaw rather than a magical one.
The demon's clinching argument is a job description. You cannot be a firelighter and a patrolman, because the establishment does not work that way.
It is the best possible objection and it comes from the least likely source. A creature on a lonely round with a clapper has just caught the Great Sage out on a point of internal administration.
And it is the third time this chapter that paperwork has done what violence could not. The kings of hell signed; the demons carry tallies; and now a cover story is collapsing on the duty roster.