bhavatu nāma nityasya vacasaḥ sambhavastathāpi na tasyātīndriyārthapratipattiṃ prati kāraṇabhāvo yuktam ityetat pratipādayann āha nityasyetyādi
Even if eternal words were possible, still their causality with respect to the comprehension of supersensuous objects would not be logical - explaining this, he says "of the eternal [word]" etc.