…for all devotional service, the main pillar is sravanam, hearing. Without hearing, other processes of devotional service will not be perfect. Therefore hearing is most important. Hearing, according to our Vaisnava philosophy, especially Lord Caitanya's, this hearing and chanting are two main pillars for devotional service.
>>> Ref. VedaBase => Bhagavad-gita 3.18-30 — Los Angeles, December 30, 1968