好借好還 Well Borrowed, Well Returned
卻說行者取了辟火罩，一觔斗送上南天門，交與廣目天王道：「謝借，謝借。」天王收了道：「大聖至誠了。我正愁你不還我的寶貝，無處尋討，且喜就送來也。」行者道：「老孫可是那當面騙物之人？這叫做『好借好還，再借不難』。」天王道：「許久不面，請到宮少坐一時，何如？」行者道：「老孫比在前不同，爛板凳，高談闊論了；如今保唐僧，不得身閑。容敘，容敘。」急辭別墜雲，又見那太陽星上。徑來到禪堂前，搖身一變，變做個蜜蜂兒，飛將進去，現了本像看時，那師父還沉睡哩。却说行者取了辟火罩，一觔斗送上南天门，交与广目天王道：「谢借，谢借。」天王收了道：「大圣至诚了。我正愁你不还我的宝贝，无处寻讨，且喜就送来也。」行者道：「老孙可是那当面骗物之人？这叫做『好借好还，再借不难』。」天王道：「许久不面，请到宫少坐一时，何如？」行者道：「老孙比在前不同，烂板凳，高谈阔论了；如今保唐僧，不得身闲。容叙，容叙。」急辞别坠云，又见那太阳星上。径来到禅堂前，摇身一变，变做个蜜蜂儿，飞将进去，现了本像看时，那师父还沉睡哩。
逐句解 Line by line
Now, the Pilgrim took up the fire-shield and with one somersault sent it back to the Southern Gate of Heaven, handing it to the Broad-Eyed Deva King. "Thanks for the loan, thanks for the loan."
觔斗, the somersault; 斗 is dǒu. The shield goes back before the ashes are cold, and the first words he says in Heaven are thanks.
The Deva King took it back. "The Great Sage is a man of his word. I was just worrying that you would not return my treasure, and that I should have nowhere to go after it — and here you are, bringing it back. I am glad."
不還我的寶貝 — 還 is huán, "to give back." The Deva King admits, to his face, that he had expected to be robbed. He is speaking to the creature who once walked off with the Dragon King's cudgel, Laozi's elixir and the peaches of the Queen Mother.
The Pilgrim said, "Is old Sun the sort of man who cheats another to his face? This is what they call: borrow well and return well, and borrowing again is easy."
當面騙物 is "to cheat a man of his goods to his face"; 當 is dāng. And then the proverb: 好借好還，再借不難, "borrow well and return well, and the next loan comes easy" — a household saying about credit, and still exactly what a Chinese parent tells a child about other people's belongings. 還 is again huán. Wukong keeps a promise about a borrowed thing on the very morning a monk's identical promise has been broken.
The Deva King said, "It is long since I saw you. Come to the palace and sit a while — what do you say?"
許久不面 is "long unseen face to face." 少坐 takes shǎo, "a little while." Heaven would like to entertain him.
The Pilgrim said, "Old Sun is not what he was before, sprawling on a broken bench and talking grandly at large. Now I am guarding the Tang monk, and I have no leisure. Another time, another time."
爛板凳，高談闊論 — "a broken bench and lofty talk" — is a wonderfully exact image of his old idleness among the gods, the immortal equivalent of holding forth in the pub. 不得身閑 takes dé. The Great Sage declines a seat in Heaven on the grounds that he has a job.
He took a hasty leave and dropped down on his cloud; and the sun-star was rising again.
太陽星上: the sun-star rising. The night is over. Only the accounting remains.
Coming straight before the meditation hall, he shook his body, turned himself into a bee,
蜜蜂兒, with the neutral er. He comes back as he left, by the same transformation — the whole night bracketed, at both ends, by a bee.
flew in, resumed his own form, and looked: his master was still fast asleep.
還沉睡哩: 還 is hái, "still." Two hundred men have lost everything they own, a demon has stolen a treasure out of Heaven, a monastery has burned to the ground — and the Tang monk has not woken up. It is the funniest and the bleakest sentence in the chapter.
The chapter sets this scene directly against the loan of the cassock, and the parallel is exact enough to be a rebuke. A treasure is borrowed on a promise. It is used. It is returned at once, before anyone asks for it, with thanks — 謝借，謝借 — and the lender confesses he had not expected to see it again. 好借好還，再借不難: borrow well, return well, and the next loan is easy. In the ruins below, an old monk who said 明早送還老爺西去 is sifting ashes, and the robe he promised to return is on its way to Black Wind Mountain.
And Wukong, of all creatures, is the one who observes the etiquette of borrowing. He declines a seat in Heaven because he has work: 如今保唐僧，不得身閑. He remembers what he used to be — 爛板凳，高談闊論, sprawled on a broken bench talking grandly — and is no longer. The fillet is doing its work. And yet the shield he returns so scrupulously is the shield he used to make certain a monastery burned, and the Deva King who praises his honesty is the god who told him, laughing, that he raises an unkind heart. Wú Chéng'ēn does not resolve this. He simply lets the sun come up on it, and sends his hero back through a window as a bee, to find his master asleep.