看樣造作 Left Out as Patterns to Copy
次日請行者三人將金箍棒、九齒鈀、降妖杖，都取出放在篷廠之間，看樣造作。遂此晝夜不收。次日请行者三人将金箍棒、九齿钯、降妖杖，都取出放在篷厂之间，看样造作。遂此昼夜不收。
逐句解 Line by line
The next day they asked Pilgrim and the other two to bring out the gold-banded rod, the nine-toothed rake and the demon-quelling staff, and set them down in the shed to be copied from.
The three weapons are named together for the last time in the chapter, in their fixed order. 降 is xiáng, subduing — the eleventh and final appearance of the character. 看樣造作 is to work from a model in front of you, which requires the model to stay there. The sentence is entirely reasonable and it is the mistake.
And so they were left out day and night, and not put away.
Six characters, and every one of them is the disaster. 晝夜, day and night; 不收, not gathered in. Bajie said yesterday that these weapons were needed to subdue demons, and here they are lying in a shed with nobody watching.
The pilgrims hand over the three weapons to be used as patterns, which is the only way copies can be made and is also the one thing they should not have done.
The last clause is six characters long and it is the hinge of the whole chapter. Not put away, day or night.
Nothing here is careless in the ordinary sense. Everyone is doing the sensible thing, and the sensible thing turns out to be the opening a demon has been waiting for.