śabdamātramathocyeta, sādhyadharmitveneti śeṣaḥ / tataś ca śabdatvasāmānaṃ vo yuṣmākam anityam, prāpnotītyadhyāhāryam /
If mere śabda were stated [as the subject of the proposition] - the word "as the subject" is to be supplied - then for you the universal śabdatva would become non-eternal - the phrase "would become" is to be supplied.