封鎖不動 The Seals Have Not Been Broken
見那封鎖不動，梆鈴不絕。問外邊巡夜的道：「唐僧從那裡走了？」俱道：「不曾走出人來。」急趕至後宰門，封鎖、梆鈴，一如前門。见那封锁不动，梆铃不绝。问外边巡夜的道：「唐僧从那里走了？」俱道：「不曾走出人来。」急赶至后宰门，封锁、梆铃，一如前门。
逐句解 Line by line
They saw the seal and lock undisturbed and the rattle and bell going without a break.
The paper seal is doing its work. Ten characters, and they prove a negative: nothing has been opened here.
They asked the night patrol outside, "Which way did the Tang Monk get out?"
那 is nǎ here, the questioning reading, not the nà of that or those. The whole line is a question about direction, and the character has to carry it.
They all said, "Nobody has come out at all."
Eight characters, and it is the truth, and it is the most damaging thing said in the chapter.
They hurried on to the Rear-Steward Gate: seal, lock, rattle and bell, all exactly as at the front gate.
一如前門, just as at the front gate — the sentence mirrors the earlier pair of gates, and closes the box.
The seals are the trap and they work perfectly, which is the cruel joke of the passage. The demons check the exits, find them untouched, and learn that the pilgrims must still be inside the walls.
The patrol tells the truth and the truth convicts. Nobody has come out is a statement of fact, and it converts a hunt across a whole countryside into a search of one enclosed city.
And notice what secured the city: not the lock but the paper. A lock keeps you in only while it holds. A seal is a record, and it goes on telling the truth about who has passed long after anyone could have stopped them.