天牌傳旨意 Summoned by the Gold Tablet
老師父緩觀山景，忽聞啼鳥之聲，又起思鄉之念，兜馬叫道：「徒弟！老师父缓观山景，忽闻啼鸟之声，又起思乡之念，兜马叫道：「徒弟！
逐句解 Line by line
The old master took in the mountain scenery slowly, and hearing all at once the cries of the birds, his longing for home rose in him again. He reined in his horse and called out, "Disciples!
The homesickness arrives through the ear, not the eye. He has been looking at the mountain contentedly enough; it is birdsong that undoes him.
From the heavenly tablet the imperial will came down to me; / beneath the brocade screen I received the travel rescript.
The 關文 is the passport the party must have stamped at every border, and it will matter again before this chapter is out. The 天牌 is the summons-board of the imperial court, so the couplet is saying, in the highest possible register, "I was called in and given my papers."
On the fifteenth, at the Lantern Feast, I left the Land of the East; / only then did I part from the Tang king, as heaven parts from earth.
The fifteenth of the first month is the Lantern Festival, the close of the New Year — so he is naming not just a date but the last cheerful day he had. 天地分, "heaven and earth parted," is a large phrase for saying goodbye to a monarch, and it is meant to be.
Tripitaka's homesickness is a running feature of the book, and his disciples treat it roughly the way a family treats a relative's familiar complaint. What makes this outburst different is its form: he does not grumble, he composes. Reining in the horse and delivering eight lines of regulated verse is a court official's way of being upset.
The verse is doing something quietly clever with time. He dates his departure exactly — the Lantern Festival, the fifteenth — and then measures the distance from it in a cosmic image, heaven splitting from earth. Precise about the beginning, hopeless about the middle, which is what being a long way from home actually feels like.