Our mind is immensely effected by what we hear.
Performing kirtana and hearing the vibration of the sound Hare Krishna is actually seeing the Supreme Personality of Godhead directly.
Purport on Srimad Bhagavatam 7.4.25-26
In this horrible condition of life there is only one way of liberation—to engage in the activities of transcendental chanting and hearing of the holy name of the Supreme Lord.
Purport on Srimad Bhagavatam 4.7.44
The main purpose of sannyasa life is to be in constant companionship with the Supreme Lord, either by thinking of Him within the heart or hearing of Him through aural reception.
Purport on SB 3.24.35
When a Vedic mantra is chanted within the mouth so that only the chanter can hear, the chanting is called japa. But when such mantras are chanted loudly, it is called kirtana.
Purport on Srimad Bhagavatam 3.14.32
Srimad Bhagavatam's every syllable is a seed of transcendence. Therefore acaryas have expanded, drawn out; therefore hearing from acaryas is important.