This throne is called vyāsāsana, sitting place of Vyāsadeva. So one who is representative of Vyāsadeva, he can sit on this throne. So guru, by paramparā system, guru is seated on the vyāsāsana because he is the representative.
Śrīla Prabhupāda's lecture on Bhagavad-gītā 2.16 -- London, August 22, 1973
