見榜即道 Four Monks Read the Notice
那官道：「今日領榜，方至市口張掛，即有四個和尚，稱是東土大唐差往天竺國大雷音拜佛求經者，見榜即道能祈甘雨，特來報知。」那官道：「今日领榜，方至市口张挂，即有四个和尚，称是东土大唐差往天竺国大雷音拜佛求经者，见榜即道能祈甘雨，特来报知。」
逐句解 Line by line
The officer said, "Today we collected the notice and had only just got to the market square to hang it up when four monks appeared. They say they are sent from the Great Tang in the Land of the East to India, to the Great Thunderclap Monastery, to worship the Buddha and seek scriptures. They read the notice and said straight out that they could pray down a sweet rain, so I have come at once to report it."
方至 means had only just got to. The messenger is doing what messengers do — reciting the sequence of events with all the timing left in, because the timing is the remarkable part. 和尚 is the ordinary everyday word for a Buddhist monk, and it is the only time it appears in this chapter; everywhere else the pilgrims are named or given titles. Coming from a junior official who does not know who they are, the plain word is exactly right.
A single long breathless sentence, and the novel gives it a whole passage because the shape of it is the joke: the man is talking too fast to punctuate.
Notice how much of the pilgrims' formal credential survives being passed along by a stranger. He has retained the Great Tang, the Land of the East, India, the monastery, the scriptures — the whole chain, delivered secondhand at speed. And then he lands on the only part his master cares about: they said they could bring rain.