去迎師兄 Which Of You Will Go
三藏道：「悟空是個會走路的，往常家二千里路，一霎時便回，怎麼如今去了一日？斷是與那牛王賭鬥。」叫：「悟能、悟淨，你兩個，那一個去迎你師兄一迎？倘或遇敵，就當用力相助，求得扇子來，解我煩躁，早早過山，趕路去也。」三藏道：「悟空是个会走路的，往常家二千里路，一霎时便回，怎么如今去了一日？断是与那牛王赌斗。」叫：「悟能、悟净，你两个，那一个去迎你师兄一迎？倘或遇敌，就当用力相助，求得扇子来，解我烦躁，早早过山，赶路去也。」
逐句解 Line by line
Tripitaka said: "Wukong is one who can travel. Ordinarily he goes two thousand lǐ and is back in a moment. How is it that he has been gone a whole day now?
Tripitaka does arithmetic, which is rarer than you might think. 三藏 takes 藏 at zàng, the Piṭaka of the name, against the cáng of 鬼神藏 ten lines earlier: both readings stand inside these few passages, which is why the character can never be taken on trust. 往常家 uses a vernacular ending 家, kept at full tone jiā. (一 shifts to yí in 一霎時, before the falling tone of 霎.)
"He must certainly be contending with that Bull King."
斷是 asserts flatly — he must certainly be fighting. The deduction rests on the one thing the master can observe from where he is sitting, which is time passing.
He called: "Wuneng, Wujing — you two: which of you will go and meet your elder brother?
那一個 is the question word, nǎ, "which one" — not the pointing reading the bare character would give. It is the third such site in the chapter, after 你往那裡去 and 孫大聖那知真假, and the least visible of the three, since here it stands before a number rather than before 裡 or a verb.
"Should you meet the enemy, lend your strength; get the fan and bring it, relieve me of this vexation, and let us be over the mountain early and away on the road."
求得扇子來 takes dé, the verb of obtaining with its object actually got, against the light linking de of 狠得他爆躁如雷 a few passages back. 解 is jiě, to loosen or relieve; 當 is dāng in 就當, "then you should".
Tripitaka's reasoning is arithmetical and rather good. Wukong covers two thousand lǐ in a moment; he has been gone a day; therefore he is fighting. The master is not often given a deduction to make in this novel, and when he is, it usually turns on the one thing he can observe from where he sits.
那一個去迎你師兄一迎 is put as a question to two disciples rather than an order to one, and the question is left hanging. Neither answers. The gap is what the next passage fills, and it gets filled by Eight Rules volunteering rather than by Tripitaka choosing.
The instructions that follow are practical and faintly self-regarding: help if there is a fight, get the fan, 解我煩躁 — relieve my vexation — and let us be over the mountain early. The last two clauses give the errand its real motive, and the chapter is quite content to let a cosmic contest resume because a man is too hot.