調虎離山 Luring The Tiger Downhill
三魔又笑道：「二位兄長在上：那和尚倘不要我們送，只這等瞞過去，還是他的造化；若要送，不知正中了我的調虎離山之計哩。」老怪道：「何為『調虎離山』？」三魔又笑道：「二位兄长在上：那和尚倘不要我们送，只这等瞒过去，还是他的造化；若要送，不知正中了我的调虎离山之计哩。」老怪道：「何为『调虎离山』？」
逐句解 Line by line
The third fiend laughed again: "My two elder brothers, hear me. If the monk does not want us to send him, and we get away with it as easily as that, it is his good fortune;
那 reads nà and 和 is hé in 和尚. 還 keeps hái, meaning even so. 造化 is luck, what fortune has made for you.
but if he does want it, then he walks straight into my plan for luring the tiger away from the mountain."
中 reads zhòng — to be struck by, to walk into something. The commoner zhōng, meaning the middle, is a different word. 調 is diào, to move something from its place.
The old fiend said: "What is this luring the tiger away from the mountain?"
為 reads wéi, the verb to be — what is meant by. The other reading, wèi, means for the sake of and does not fit here.
The stratagem has a name, and the name is the whole idea: get the tiger to leave the mountain. A tiger on its own ground is unbeatable; the same animal on open plain is just a large cat. You do not fight it, you persuade it to move.
It sits in the traditional list of military ruses alongside the goading stratagem the third fiend used on Wukong at the start of the chapter, and the repetition is not accidental. This demon does not fight. He identifies what protects his opponent and then arranges for the opponent to give it up voluntarily.
What makes the line frightening is the first half of it. If the monk refuses our escort, he says, that is simply his luck — meaning the trap costs nothing if it fails. He has built a plan that only ever gains, and the pilgrims are about to accept the escort.