gaṅgāra mahattva - glorification of mother Ganges; śloke - in the verse; mūla - chief; vidheya - unknown; idam śabde - by the word idam ('this'); anuvāda - the known; pāche - at the end; avidheya - improper.

“The glorification of the Ganges [mahattvaṁ gaṅgāyāḥ] is the principal unknown subject matter in this verse, and the known subject matter is indicated by the word ‘idam,’ which has been placed after the unknown.