Srimad BhagavadGita

After elaborating on how meditating on HIS divine auspicious form clears the anyonyāśraya doṣa, in this śloka, Kṛṣṇa describes the path to the ultimate objective of human pursuit called mokṣa. When one's mind becomes pure, he obtains a vision of the soul. As a result of this vision, the ultimate objective which is freedom from all the miseries originating from contact with this material world is achieved. Kṛṣṇa says to Arjuna, "All the miseries of such a person get destroyed after the mind gets purified and very soon his intelligence becomes well established."

asya prasāde (When his mind is purified by following the process described earlier) 

sarva-duḥkhānāṃ hāniḥ upajāyate  (All the miseries get destroyed for the practitioner) duḥkhājñānamalādharmāḥ prakrtuteḥ te na cātmanaḥ Viṣṇu Purāṇa 6-7-22 The characteristics like misery, ignorance, impurities, etc, come to the soul solely due to its contact with material world. These are not the natural characteristics of the soul.) As told in the above statement, all the mentioned characteristics imposed on the soul due to its contact with the material world get destroyed.

Q: How does the purification of the mind completely destroy all the miseries of the material world?  

A: This question is answered in the second half of the śloka as follows,

prasanna-cetasaḥ (The practitioner whose mind is cleared of all the shortcomings which are hurdles in

obtaining a vision of the soul)

āśu (very soon) 

buddhiḥ paryavatiṣṭhate hi (obtains a vision of this soul which is different from the body, in a stable

manner)

hi  In this way, purification of the mind results in a vision of the soul which further results in bhakti yoga. As

a reward of bhakti yoga, mokṣa which is the permanent destruction of all the miseries, is obtained. Thus

mokṣa is the ultimate reward of purification of the mind.