結為兄弟 The King Pleads, the Monk Demurs
那國王聞言，急回頭，便請三藏道：「長老若有手段，放法力，捉了妖魔，救我孩兒回朝，也不須上西方拜佛，長髮留頭，朕與你結為兄弟，同坐龍床，共享富貴如何？」三藏慌忙啟上道：「貧僧粗知念佛，其實不會降妖。」國王道：「你既不會降妖，怎麼敢上西天拜佛？」那国王闻言，急回头，便请三藏道：「长老若有手段，放法力，捉了妖魔，救我孩儿回朝，也不须上西方拜佛，长发留头，朕与你结为兄弟，同坐龙床，共享富贵如何？」三藏慌忙启上道：「贫僧粗知念佛，其实不会降妖。」国王道：「你既不会降妖，怎么敢上西天拜佛？」
逐句解 Line by line
Hearing this, the king turned quickly about and entreated Tripitaka: 'Elder, if you have the skill — if you would loose your power to take the demon and bring my child back to the court — then you need not go west to worship the Buddha at all. Grow out your hair, keep a full head, and I shall bind myself to you as a sworn brother; we shall sit together upon the dragon-couch and share its riches. What say you?'
The king offers everything at once, which is what desperation sounds like. 手段 is skill or means; 放法力 is to loose one's magic power; 救我孩兒 takes 兒 as the noun ér, my child. The startling item is 長髮留頭 (長 = zhǎng, to grow): grow the hair out, keep a full head — that is, stop being a monk. A shaved head is the vocation, so this is an offer to buy Tripitaka out of it. 結為兄弟 (為 = wéi) is to swear brotherhood. A throne, a fortune, and a brother, in exchange for one demon.
Tripitaka hastily replied, 'This humble monk knows only, and roughly, how to recite the Buddha's name; in truth I have no skill to subdue demons.'
粗知念佛 is "I know, roughly, how to recite the Buddha's name" — and it is the plain truth rather than modesty. 降妖 (降 = xiáng), subduing demons, has never been his department. It will not save him.
Said the king, 'If you cannot subdue demons, how did you dare set out for the Western Heaven to worship the Buddha?'
The king puts his finger on what looks like an obvious contradiction: a man with no defences does not set out across demon country. He is right, of course — and pressing the point is exactly what forces Tripitaka to admit he has not been travelling alone.
The king's offer is a small drama of temptation. In his desperation he holds out everything a worldly heart might want — sworn brotherhood with a king, a seat on the dragon-couch, a share of the treasury — and, most pointedly, release from the pilgrimage itself: grow your hair out, keep a full head, give up the shaven vocation and come back to the world. The proposal is born of grief rather than malice, but it sets the secular life in its most attractive form against the monk's austere errand, and Tripitaka's unbothered refusal quietly settles where his commitment lies.
His demurral is also, as usual, literally true. Tripitaka really cannot subdue demons; that work belongs to his disciples, and he himself knows only, and roughly, how to recite the Buddha's name. But the king's blunt logic — how, then, did he dare start such a journey? — will not let the truth stand as a refusal. It pushes him toward the one disclosure he has been trying to avoid: that he travels with two companions of deeply alarming appearance.