現了本相 He Shows His True Form
卻說行者飛出去，現了本相，到於洞口，叫聲：「開門！」八戒笑道：「沙僧，哥哥來了。」他二人撒開兵器。却说行者飞出去，现了本相，到于洞口，叫声：「开门！」八戒笑道：「沙僧，哥哥来了。」他二人撒开兵器。
逐句解 Line by line
Now Pilgrim flew out, showed his true form, came to the mouth of the cave and called, "Open up!"
The narrator resets the scene with 卻說, the storyteller's now then — we leave one thread and pick up another. 本相 is a creature's original shape, the thing a transformation covers, and 相 in it is xiàng, the noun reading for form, not the xiāng of mutual.
Bajie laughed. "Sha Monk, brother is back."
Ten characters of relief. Bajie has been standing at a hole in a rock for a long stretch of the chapter with nothing to do but wait.
The two of them spread their weapons apart.
They have been blocking the entrance since Pilgrim ordered it, and they open the way without being asked. It is a small sign that the plan is holding.
The scene cuts from a wrecked banquet three hundred lǐ underground to two disciples standing at a hole in a rock. The novel does its transitions with a single formula and no fuss.
The detail worth catching is that Bajie and Sha Monk have done exactly what they were told and are still doing it. They have held the door through the whole of the cave sequence, and the story has not looked at them once.