樹成了精 This Tree Has Become A Spirit
他道：「這顆樹成了精也，這顆樹成了精也。」八戒舉鈀，又正築處，只見行者引怪出來。那獃子不打話，趕上前，舉鈀就築。他道：「这颗树成了精也，这颗树成了精也。」八戒举钯，又正筑处，只见行者引怪出来。那呆子不打话，赶上前，举钯就筑。
逐句解 Line by line
He said, "This tree has become a spirit! This tree has become a spirit!"
The doubled line is the novel's mark of somebody with one thought and no words left over — the terrified king said "take them away" twice, and Bajie says this. The difference is that Bajie is pleased. 成精, becoming a spirit, is the standard folk explanation for anything old behaving oddly: given enough years, a tree, a fox or a stone can start to cultivate and take on powers.
Bajie raised his rake and was just going to dig again when he saw Pilgrim bringing the fiend out.
The timing is the joke. He is winding up for another swing at a wounded tree at the exact moment the actual enemy walks out of the door he was posted to watch.
The blockhead did not stop to talk, but ran up and struck with the rake.
不打話 — not stopping to exchange words — is significant given what has just happened in verse. Wukong and the fiend argued for eleven lines about compassion and jurisdiction; Bajie arrives and swings. The novel puts the two approaches side by side and does not say which it prefers.
Bajie is not, in fact, wrong. He was told to stand ready and take the fiend as he came out, and that is exactly what he does, the instant it becomes possible. The tree was a way of passing the time.
The comedy is in the sequencing rather than in any failure. He spends the fight assaulting scenery, makes an absurd announcement about it, and then executes his orders perfectly. That combination is Bajie in miniature, and the novel has been running it for seventy-nine chapters without it going stale.