There is nothing in this world so purifying as jñāna. In due course of time, one will automatically attain it in himself, by dint of the maturity and fruition of yoga pursuit.
Krishna is extolling the nature and effect of spiritual wisdom, jñāna. Purity of mind is imperative in pursuing jñāna. How to bring this inner purity?
Many resort to rituals, ceremonies, worship and the like for gaining the desired purity. How can rituals and ceremonies, which are more acts and expressions, directly touch and improve the mind? So, effective means will be to get to the mind directly and instil purity.
Krishna says the very hearing and reflection of spiritual truths will imbue purity and sublimity to the inner being. Arjuna illustrates this best. Compared to the long austere forest-exile and incognito life, what is this short spell of dialogue? But every word purifies Arjuna!
Inner purity paves the way for yogic perfection. In due course, the seeker realizes the Self in all its amplitude in himself. In place of fear and doubt, it is steady and invincible direct personal realization now!