敦煌莫高窟254窟，為北魏時期鑿建的，平面為方型，中央後方有一大形四方柱。前方為橫長形的敞開空間，（頂部）為橫向的人字披頂，左（北）壁之空間，為一鋪大型佛說法圖，（該鋪說法圖）即是本文的研究（對象）。至今的研究，乃是依據位於壁畫底部，佛陀二側的人物，認為該壁畫是表現難陀出家因緣。然而，我認為此說法並不正確。本文中，我重新分析該壁畫的（人物）形樣，釐清主題及依據之文本，並且討論該壁畫在其石窟的脈絡及其空間配置。首先，為了釐清該壁畫的主要題材，我聚焦於該壁畫的主要三尊像，包括說法的佛陀、持金剛神及一位比丘。同時，我們發現在佛陀後面有一個如石窟般大的拱門、佛陀足前有二龍王位於方形池塘中、背景的小石窟中有諸多僧眾禪坐著及一位婆羅門。依據呈現於此的諸人物形樣，我認為此畫可能依據的文本，為《觀佛三昧海經》第七卷的〈觀四威儀品〉。該經敘述佛陀在那乾訶羅國降伏龍王，並留下祂的影子在龍洞中。此外，在該窟前方人字披頂處，該壁畫是相對著右（北）壁的〈佛陀降魔圖〉。在莫高窟其他被斷代為相同時期且有中心柱的石窟中，繪製〈佛陀降魔圖〉壁面之對壁，常安置著〈佛陀初轉法輪圖〉。在該壁畫（莫高窟254窟北壁） 位於〈佛陀初轉法輪圖〉相對位置的圖像，則是選擇「那乾訶羅國佛陀降伏龍王」，取代「佛陀降魔」。我認為〈初轉法輪圖〉轉變成此新題材的重要因素之一，是位於該窟中心柱後壁的「白衣佛畫」。「白衣佛」極可能是表現在龍洞之佛影，由龍洞之佛影可揭示出「白衣佛」與該窟前部方的關連。並且，我認為該窟前壁兩兩相對的〈薩埵太子本生〉以及〈尸毗王本生〉，亦是依據同一部經典。因此，我可以說該窟五鋪壁畫的主題彼此間有著緊密的關聯。再者，無法令人忽略的事實是，該經（《觀佛三昧海經》）第一卷描述有佛陀的行跡，佛陀在那乾訶羅國降伏毒龍以及在龍洞中留下佛影，是被當作佛一生的重要事件之一，接續在誕生、結婚、出家、降魔、成道之後。事實上，該故事指出人們並不知道佛陀可以藉由祂的影子製造意象。我認為如同降魔以及初轉法輪，該壁畫的主題亦被視為關於佛一生的重要事件之一。很重要的是，僅有該經（《觀佛三昧海經》）有將此故事作為佛一生的重要事件之一。最後，該窟前部的空間安置著佛陀塑像。而該壁畫及對向的〈降魔圖〉，不斷地提醒該窟中禮拜的人們，彼等所禮敬的主尊像，乃是歷史上正在說法的佛陀。

Mogao Cave 254 at Dunhuang, which was constructed in the Northern Wei, has a rectangular plan with a large square pillar in the center of the rear section. The front section comprises a rectangular open space with a transverse gabled ceiling, and on the left (north) wall of that space, there is a large wall painting of the Buddha preaching, which is the subject of this study. Up to this time, based on the figures that appear at the bottom of the wall painting on both sides of the Buddha, it was thought that this painting represented the Nanda Avadāna. However, I suspect that this identification is not correct. In this paper, I analyze again the imagery in the painting, to clarify the themes and the text on which it was based. Additionally, I touch on the function of this painting in the context of this cave and the spatial arrangement of its paintings. First, in order to clarify this picture’s principal theme, I focus on the main trinity in this picture, which consists of a preaching Buddha, Vajrapāni and a monk. In addition, we find a big cave-like arch behind the Buddha, a square pond with two dragon kings (nāgarājas) at his feet, a number of disciples meditating in small caves in the background, and one brāhmana. In light of the various figures represented here, I would like to point out the possibility that this wall painting is based on the chapter, “The Visualization of the four types of deportments of the Buddha,” from the seventh volume of The sūtra on the Ocean-Like Samādhi of the Visualization of the Buddha, in which it is said that the Buddha subdued some dragons (nāgas) at Nagarahāra and left his shadow on the wall of the nāgas’ cave. Furthermore, in the front gabled-space of the cave, this painting is opposite the right (south) wall painting of the Buddha subduing demons. In other Mogao caves with a square central pillar which date from the same period, the wall painting of the subjugation of the demons is usually placed opposite the wall painting of the first Turning of the Wheel of the Dharma. Therefore, in this case the scene of the subduing of dragons at Nagarahāra was chosen instead of the scene of the first Turning of the Wheel, to stand opposite the subduing of demons. I think that one of the primary factors that explains the change from the scene of first Turning the Wheel to this new subject is the painting of the “White-Robed Buddha” in the center of the rear wall of the cave. There is a strong possibility that this White-Robed Buddha represents the Buddha’s shadow on the nāgas’ cave, which indicates a connection between the “White-Robed Buddha” and the painting at the front of the cave. Moreover, I think that the scenes of the Mahasattva Jātaka and Sibi Jātaka that face each other in that same front space were based on the identical sutra. Therefore I can say that the themes of the five wall paintings in this cave are closely connected with one another.
Additionally, in the chapter “The enumeration of the objects of visualization,” which is the first volume of that sutra, I cannot overlook the fact that following the scenes of the Birth, the Marriage, the Renunciation of the World, the Subduing of Demons, and the Enlightenment, the story of the subjugation of dragons at Nagarahāra and the leaving of the Buddha’s shadow in the nāgas’ cave is mentioned as one of the main episodes of the Buddha’s life. The point of the story is that the people who do not know the Buddha himself can make an image of him based on his shadow. Therefore I think that, like the subduing of demons and the first Turning the Wheel, the subject of this painting was regarded as one of the main scenes of the Buddha’s life. And it is important that only this sutra includes this story as one of the main episodes in the life of the Buddha. Finally, the front space of the cave functioned as the space where offerings could be made to the main Buddha statue in the cave. Thus, together with the wall painting, “Subduing of demons,” this painting which is facing it reminds people who worship the main Buddha statue of the history of the preaching Buddha.