錯拿難送 Wrongly Taken, Not Lightly Returned
眾妖道：「這等說，唐僧吃不成，卻不把豬八戒錯拿了？如今送還他罷。」二魔道：「拿便也不曾錯拿，送便也不好輕送。唐僧終是要吃，只是眼下還尚不能。」眾妖道：「這般說，還過幾年麼？」二魔道：「也不消幾年。众妖道：「这等说，唐僧吃不成，却不把猪八戒错拿了？如今送还他罢。」二魔道：「拿便也不曾错拿，送便也不好轻送。唐僧终是要吃，只是眼下还尚不能。」众妖道：「这般说，还过几年么？」二魔道：「也不消几年。
逐句解 Line by line
The imps said: "By that reckoning, if Tripitaka can't be eaten, then wasn't Zhu Bajie taken in error after all?
這等說 (zhè děng shuō), "put that way, by that account." The frame 卻不...了 builds a rhetorical "then isn't it the case that...," and the imps use it to reach the awkward conclusion their captain has been avoiding.
"Best send him back to them now."
送還 (sòng huán), "to send back" -- 還 read huán, "to give back," not the hái of "still." The chapter puts both readings in one sentence a few scenes from here. The closing 罷 (ba) is the "let's" particle.
The second fiend said: "As for the taking, it was no error to take him; as for the sending, it would not do to send him back so lightly.
A balanced pair, 拿便...送便..., "as for taking... as for sending..." -- the demon weighing two courses in matching clauses. 輕送 (qīng sòng) is to give something back too cheaply, to hand over a prize for nothing.
"Tripitaka is to be eaten in the end — it is only that, for the present, we still cannot yet manage it."
終是 (zhōng shì), "in the end, when all is said." 還尚 (hái shàng) stacks two words for "still" on top of each other -- 還 here is hái, and the doubling stretches the delay out.
The imps said: "Put that way, must we wait some years yet?"
還過幾年 (hái guò jǐ nián), "wait out a few more years yet," 還 again hái. The 麼 (me) makes it a question, and a slightly appalled one.
The second fiend said: "It won't take years, either.
不消 (bù xiāo), "no need, it won't take" -- 消 in its sense of using something up. A brisk brush-off of the imps' impatience, and a hook: he clearly has a date in mind.
The imps reason their way to a dead end. If the master cannot be eaten, the pig is dead weight, so give him back. Their captain refuses both halves -- taking him was no mistake, and returning him would be throwing away a card. His formula is deferral, not surrender: Tripitaka will be eaten in the end, only not yet.
The exchange sets a patient villain against impatient followers. Where the imps think in terms of an immediate ledger -- catch, cost, cut the loss -- their captain is working to a longer plan, and his curt "it won't take years either" both silences them and dangles the scheme he is about to reveal. The craft is in holding it back one beat longer.