肉眼凡胎 Mortal Eyes See No Plot
眾妖叩首道：「請老爺上轎。」那三藏肉眼凡胎，不知是計。孫大聖又是太乙金仙，忠正之性，只以為擒縱之功，降了妖怪，亦豈期他都有異謀？卻也不曾詳察，盡著師父之意。众妖叩首道：「请老爷上轿。」那三藏肉眼凡胎，不知是计。孙大圣又是太乙金仙，忠正之性，只以为擒纵之功，降了妖怪，亦岂期他都有异谋？却也不曾详察，尽着师父之意。
逐句解 Line by line
The demons bowed their heads and said: "Will your reverence take the chair."
叩首 — to knock the head, the deepest of the salutes.
Now Tripitaka was of mortal eye and common flesh, and did not know it was a trick.
肉眼凡胎 — eyes of flesh and an ordinary body, the standing phrase for someone who cannot see past appearances.
And the Great Sage Sun, being besides a Golden Immortal of the Great Monad and of an upright nature, took it only that his work of taking and releasing had subdued the monsters, and how should he have expected that they all had a further design?
為 reads wéi in 以為, to take it that; 降 reads xiáng, to subdue. Each character has a commoner reading that does not fit. 太乙金仙 is a high immortal rank.
So he too made no close inquiry, and gave way entirely to his master's wish.
著 reads zhe in 盡著 — going along with, all the way.
The novel stops the action to allocate blame, and it does so with unusual care. Tripitaka is excused on the grounds of being human: eyes of flesh, an ordinary body, no way of seeing through anything. That is not a criticism, it is a description of the species.
Wukong gets a longer defence and it is the more interesting one. He is a high immortal and, the narrator says, upright by nature — and it is precisely the uprightness that fails him. Having taken the demons and released them, he assumes the transaction is closed, because that is how it would work if everyone meant what they said.
The last line is the damning one. He made no close inquiry, and gave way entirely to his master's wish. Wukong has spent the whole chapter overriding Tripitaka, mocking him, and doing exactly as he pleased. The one time he defers is the time it costs them everything.