金光明最勝王經疏 4.207

4.207

由七地中多住無相，以方便善巧說不可說無相之義，亦不壞假名因緣法藏。由第八地得無相功用智，以大願力能通達實語為生法則。音聲即語。

The commentary says: Because on the seventh ground one mostly abides in signlessness, by skillful means one expounds the ineffable signless meaning, yet without destroying the treasury of dharmas of conventionally designated causes and conditions. Because on the eighth ground one attains effortless signless wisdom, by the power of great vows one can penetrate true speech as the rule for beings. Sound is speech.