此一法甚善 A Very Good Method
卻說長老辭別了欽法國王，在馬上欣然道：「悟空，此一法甚善，大有功也。」沙僧道：「哥啊，是那裡尋這許多整容匠，連夜剃這許多頭？」却说长老辞别了钦法国王，在马上欣然道：「悟空，此一法甚善，大有功也。」沙僧道：「哥啊，是那里寻这许多整容匠，连夜剃这许多头？」
逐句解 Line by line
The elder took his leave of the king of the Dharma-Revering Kingdom and said cheerfully from the saddle, "Wukong, that was a very good method, and much merit has come of it."
卻說 is the storyteller picking a thread back up, the companion of the 不題 that dropped the last one. Tripitaka is cheerful, which is rare enough in this chapter to be worth marking — in about four hundred characters he will be terrified again and stay that way.
Sha Monk said, "Brother, where did you find so many barbers, to shave so many heads in one night?"
Sha Monk asks the practical question nobody else thought of, which is his usual function. 那 is nǎ here, the interrogative where, not the nà that points at something. 整容匠 — a craftsman who puts a face in order — is the Ming word for a barber.
Tripitaka calls it a method and credits it with merit, and both words are chosen. He has spent the journey worrying that his disciples solve problems by violence; this time nobody died and a kingdom converted, so the ledger is clean.
Sha Monk speaks about once a chapter and it is usually to ask how something actually worked. Here he is doing the reader's job — the logistics of shaving an entire capital overnight really do want explaining.