辨真邪 Telling True from False
這大聖聞言，即與沙僧辭了菩薩。這一去，到那：这大圣闻言，即与沙僧辞了菩萨。这一去，到那：
逐句解 Line by line
The Great Sage heard her, and took leave of the Bodhisattva together with Sha Monk.
即與沙僧辭了菩薩 puts the two of them together for the first time since the expulsion — the real Pilgrim and the disciple who tried to brain him a page ago.
And on this journey, where they were bound was:
這一去，到那：is the closing tag, at the end of an 18-graph prose line, and it opens the chapter's smallest showcase — a single couplet. 到那 is deictic 那, nà, pointing forward to the place the verse names.
Before the Mountain of Flowers and Fruit, the black shall be parted from the white; at the mouth of the Water-Curtain Cave, the true shall be told from the false.
分皂白 closes the chapter on the metaphor it opened with: Wukong's complaint at Potalaka was that his master 更不察皂白之苦, never looked into which was black and which was white, and the Bodhisattva then took the phrase up to rule against him. It returns here as the thing the next chapter must do.
A single couplet, and the chapter's smallest showcase. The two lines are strictly parallel — place, then act — and the acts are the same act said twice: 分皂白, part the black from the white, and 辨真邪, tell the true from the false.
皂白 has been the chapter's governing figure from the start. Wukong wept at Potalaka that his master would not look into which was black and which was white; the Bodhisattva took the word from him and used it to rule against him; Bajie used it of Tripitaka's refusal to sort the two. Every use so far has been about moral discrimination — telling a right act from a wrong one. Here, in the last line of the chapter's verse, the same phrase turns into a question about identity.
That is the chapter's whole movement in two lines. It began as a dispute over whether killing bandits was justified, and it ends with nobody able to say which of two identical monkeys is the real one. The moral question has not been answered; it has been replaced.