山勢崔巍 A High Mountain Blocks the Road
正歡喜處，忽見一座高山阻路。唐僧勒馬道：「徒弟們，你看這面前山勢崔巍，切須仔細。」正欢喜处，忽见一座高山阻路。唐僧勒马道：「徒弟们，你看这面前山势崔巍，切须仔细。」
逐句解 Line by line
In the very midst of their gladness a high mountain rose across the road.
The hinge of the chapter, and it is twelve characters wide. 正歡喜處 — right at the happy part — is the novel putting the good mood and the obstacle in the same sentence so you feel the one cut off the other.
The Tang Monk reined in his horse. "Disciples, look at the mountain rearing up ahead of us. We must go carefully."
勒 is lè, the reading for reining a horse — the dictionary glosses the character as a bridle. The everyday lēi, pulling a cord tight, is a different job for the same character. 仔 is zǐ in 仔細, careful. 崔巍 is a two-character word for a mountain that towers — both halves carry the height, and neither means anything much alone.
Tripitaka sees the mountain first and stops the horse. He always does. Over the journey this reflex has been wrong more often than right, and the novel keeps it anyway, because a pilgrim who was never afraid would not be making a pilgrimage.
Note the placement. Eight characters ago everyone was laughing. The book does not give the good mood a paragraph of its own to fade in; it drops the mountain on top of it.