師父登壇 The Master Mounts the Altar
行者得旨，急抽身到壇所，扯著唐僧道：「師父請上臺。」唐僧道：「徒弟，我卻不會祈雨。」八戒笑道：「他害你了，若還沒雨，拿上柴蓬，一把火了帳。」行者道：「你不會求雨，好的會念經。等我助你。」行者得旨，急抽身到坛所，扯着唐僧道：「师父请上台。」唐僧道：「徒弟，我却不会祈雨。」八戒笑道：「他害你了，若还没雨，拿上柴蓬，一把火了帐。」行者道：「你不会求雨，好的会念经。等我助你。」
逐句解 Line by line
Pilgrim, having the royal leave, quickly withdrew to the altar-ground, and tugging at the Tang Monk said, “Master, please go up onto the platform.”
得旨: 得 = dé, to receive the royal leave. 扯著: 著 = zhe, tugging and keeping hold. 行者: 行 = xíng.
The Tang Monk said, “Disciple, but I do not know how to pray for rain.”
不會祈雨: the falling tone of 會 pulls 不 to bú. Tripitaka is, as usual, the only person present telling the exact truth about his own abilities.
Bajie said with a laugh, “He has done you a bad turn — if there's still no rain, they'll pile on the kindling and settle the account with a single torch.”
害你了: 了 = le. 若還: 還 = hái. Then a small trap for the reader: 一把火了帳 has 了 = liǎo, to finish or settle -- 了帳 is "to square the account" -- and it sits two clauses away from the le above it. Same character, different word, one line apart. Bajie is saying they will be burned alive, and putting it in the language of a closed ledger.
Pilgrim said, “You cannot pray for rain, but you are good at chanting scriptures.
行者: 行 = xíng. 好的會念經 "you are the one who is good at chanting the scriptures."
Wait while I help you.”
等我助你 "wait while I lend a hand."
The plan turns out to be a division of labour. Wukong cannot pray; Tripitaka cannot make rain; but Tripitaka can chant, and chanting is all the cover the operation needs.
Bajie supplies the stakes in a joke: if no rain comes they will pile on the kindling and settle the account with one torch. He is not exaggerating -- the execution ground was in the wager -- and the flippancy is how this novel usually delivers bad news.
What we are being set up for is one of the finest images in the book: a monk sitting perfectly still in silent prayer at the top of an altar, while below him a monkey conducts the sky with a stick.