大方廣佛華嚴經疏 21.10

21.10

第二「爾時」下放光。足上謂趺背，行必動故。背依輪指得有用故，表行依信解而成用故。餘同前會。

Second, from "At that time" downward, the emission of light. "Above the feet" means the instep, because walking necessarily moves. The instep relying on the wheels and toes is able to have function, signifying that practice relies on faith and understanding to achieve function. The rest is the same as the previous assembly.