倒驗方行 Let The Document Be Verified
長老啟奏道：「臣僧乃南贍部洲東土大唐國差來拜西方天竺國大雷音寺佛，求取真經者。路經寶方，不敢擅過，有隨身關文，乞倒驗方行。」那國王聞言大喜，傳旨教宣唐朝聖僧上金鑾殿，安繡墩賜坐。長老獨自上殿，先將關文捧上，然後謝恩敢坐。长老启奏道：「臣僧乃南赡部洲东土大唐国差来拜西方天竺国大雷音寺佛，求取真经者。路经宝方，不敢擅过，有随身关文，乞倒验方行。」那国王闻言大喜，传旨教宣唐朝圣僧上金銮殿，安绣墩赐坐。长老独自上殿，先将关文捧上，然后谢恩敢坐。
逐句解 Line by line
The elder made his memorial: "Your servant the monk is one sent by the Great Tang in the Land of the East, in the Southern Continent of Jambudvipa, to worship the Buddha at the Great Thunderclap Monastery in the western kingdom of India, and to seek the true scriptures.
臣僧 is how a monk styles himself in front of a sovereign — your-servant-the-monk — acknowledging the secular authority without giving up the religious standing. 天竺 is India, and 大雷音寺 the Buddha's own monastery, which is where the whole journey is going.
"My road passes through your precious realm, and I dare not go through without leave. I have a travel document upon me, and beg that it may be verified so that I may proceed."
不敢擅過 is the polite formula for not presuming to cross a border unannounced, and it is the entire legal content of the request. 乞倒驗方行 asks for the document to be checked and countersigned before he moves on.
The king heard it with great delight, and gave the order that the holy monk of the Tang court be summoned up onto the Hall of the Golden Chariot-Bells, and an embroidered stool set for him to sit.
The delight is not explained. A king whose kingdom has lost its light and its tribute is being called on by a holy man from the Tang, and the embroidered stool is a considerable honour, offered before anything has been asked for.
The elder went up alone, first presented the travel document with both hands, and only then gave thanks and ventured to sit.
獨自 — alone, because Pilgrim has not been invited up. 先…然後 lays out the order of a correct proceeding: business first, courtesy second, and the seat last of all. 敢坐 is to venture to sit, not simply to sit down.
The memorial is a model of its kind and contains not one word about the monks in cangues, or the pagoda, or the two fiends chained up in the monastery overnight. Tripitaka states who he is, where he is going and what he wants, and then sits down. The business he came for is not yet the business he raises.
The order of operations in the last sentence is a whole court etiquette in eighteen characters: go up alone, hand the document over with both hands, thank the king, and only then take the seat that was offered before any of it. He does every part of it, and Pilgrim is standing below with his arms folded.