If you simply hear about God, then you will see God by hearing. That is... Because there is cloud of dirtiness within our heart. Unless that dirtiness is cleansed, we can't perceive God. Therefore this process of chanting Hare Krishna mantra is described by Sri Caitania Mahaprabhu, ceto-darpana marjanam (Cc. Antya 20.12) "cleansing the mirror of the heart". Just like unless you cleanse the mirror which is full of dust, you can't see your face very nicely; similarly, unless you cleanse your heart very nicely, or in other words, unless your heart is cleansed of all sinful reaction, you can't understand what is God. That is not possible.
Srimad Bhagavatam 1.2.6, Delhi, November 11, 1973