且饒你 Spared for Now
獃子沒計奈何，扯住師父道：「你替我說個方便兒。」長老道：「悟空說你編謊，我還不信，今果如此，其實該打。但如今過山少人使喚，悟空，你且饒他，待過了山。再打罷。」行者道：「古人云：『順父母言情，呼為大孝。』師父說不打，我就且饒你。你再去與他巡山，若再說謊誤事，我定一下也不饒你。」呆子没计奈何，扯住师父道：「你替我说个方便儿。」长老道：「悟空说你编谎，我还不信，今果如此，其实该打。但如今过山少人使唤，悟空，你且饶他，待过了山。再打罢。」行者道：「古人云：『顺父母言情，呼为大孝。』师父说不打，我就且饶你。你再去与他巡山，若再说谎误事，我定一下也不饶你。」
逐句解 Line by line
The blockhead, at his wits' end, clutched the Master: "Put in a good word for me."
沒計奈何, méi jì nài hé, "no scheme left and nothing to be done" — at the end of his resources. The 兒 of 方便兒 is the light er, and 說個方便 is "put in a good word," literally to speak a convenience for someone. He grabs the master, which is what he always does.
Said the Elder: "When Wukong said you'd made up lies, I did not believe it; but now it proves so, and you do indeed deserve a beating.
編謊, biān huǎng, "to weave a lie." 還 is hái; 長 is zhǎng. The master concedes the point handsomely — I did not believe him, and now it turns out he was right, and you do deserve it.
But just now, in crossing the mountain, we're short of hands to send; Wukong, spare him for the present — beat him after we've passed the mountain."
And then withdraws it, on operational grounds. 少人使喚, shǎo rén shǐ huàn, "short of hands to send"; 饒, "to let off, to spare." Beat him after we are over the mountain — a deferral that everyone in the scene understands will never be collected.
Said Pilgrim: "The ancients said: 'To yield to a parent's wish is called great filial piety.' Since the Master says not to beat you, I'll spare you for now.
Pilgrim gives way, and dresses the surrender in Confucian clothing. 順父母言情，呼為大孝, shùn fù mǔ yán qíng, hū wéi dà xiào, "to go along with a parent's wishes is called great filial devotion" — 為 read wéi, "is called." The claim is that dropping the punishment is an act of filial piety, which requires the master to be his parent and a lazy comrade to be the beneficiary. Pilgrim is having it both ways and enjoying it.
Go patrol the mountain for him again; and if you lie and wreck things once more, I'll not let you off by a single stroke."
與他巡山, yǔ tā xún shān, "patrol the mountain for him"; 誤事, "to wreck the business." The sentence is suspended, not cancelled — and the condition is that he goes back out and does the job properly.
The master steps in, and his intervention cuts both ways. He concedes fully that Pilgrim was right and that Eight Rules deserves the beating — a real admission, since he had flatly denied the charge two passages earlier — and then asks for it to be deferred on the ground that they are short-handed for the crossing. Protectiveness reasserts itself the moment it has been proved unwarranted, which is exactly what Pilgrim predicted when he complained that the master 護短, covers for him.
Pilgrim yields with a flourish of Confucian propriety, quoting the maxim that going along with a parent's wishes is great filial devotion. The joke is in the fit: the "parent" is his nominal master, and the filial act consists of not hitting a lazy colleague. His closing warning — lie again and you will not be let off by a single stroke — sends Eight Rules straight back out to the task he shirked, which is the only thing that could restart the plot. The demons, after all, are still up there waiting.