金光明經文句記 5.16

5.16

初、經家敘。先標北方天王者，西土以北方為上也。偏袒者，西方之禮，弟子詣師必須偏袒，表有執役。

First, the compiler of the sūtra narrates. First designating the Heavenly King of the North is because the Western regions take the North as supreme. Baring one shoulder is the etiquette of the Western regions: when a disciple approaches a master, they must bare one shoulder to express that they are ready to render service.