that which can only be heard of (and not be seen) —

having sounds —

meanings that are learned by listening (ṣravaṇam); —

those who have subtle knowledge through hearing —

 hearing the meanings (of such vĕdhams etc) —

 other ancillary subjects —

 ithihāsas (epics) etc —

(he) made me get such knowledge (as ī heard from his advises), —

 along with the instruction from preceptor —