na yasya cittam bahir-artha-vibhramam
tamo-guhayam ca visuddham avisat
munir vicaste nanu tatra te gatim
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The devotee whose heart has been completely cleansed by the process of devotional service and who is favored by Bhaktidevi does not become bewildered by the external energy, which is just like a dark well. Being completely cleansed of all material contamination in this way, a devotee is able to understand very happily Your name, fame, form, activities, etc.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As stated in Srimad-Bhagavatam (3.25.25):
satam prasangan mama virya-samvido
bhavanti hrt-karna-rasayanah kathah
taj-josanad asv apavarga-vartmani
sraddha ratir bhaktir anukramisyati
Simply by the association of pure devotees one can understand the transcendental name, fame, quality and activities of the Supreme Personality of Godhead. Sri Caitanya Mahaprabhu has repeatedly said:
‘sadhu-sanga’, ‘sadhu-sanga’ — sarva-sastre kaya
lava-matra sadhu-sange sarva-siddhi haya
(Cc. Madhya 22.54)
Simply by associating with a pure devotee, one becomes wonderfully advanced in Krsna consciousness. Sadhu-sanga, or association with a devotee, means always engaging in Krsna consciousness by chanting the Hare Krsna mantra and by acting for Krsna. Specifically, chanting the Hare Krsna mantra purifies one, and this chanting is therefore recommended by Sri Caitanya Mahaprabhu. Ceto-darpana-marjanam: by chanting the names of Krsna, the mirror of the heart is cleansed, and the devotee loses interest in everything external. When one is influenced by the external energy of the Lord, his heart is impure. When one’s heart is not pure, he cannot see how things are related to the Supreme Personality of Godhead. Idam hi visvam bhagavan ivetarah (Bhag. 1.5.20). He whose heart is purified can see that the whole cosmic manifestation is but the Supreme Personality of Godhead, but he whose heart is contaminated sees things differently. Therefore by sat-sanga, or association with devotees, one becomes perfectly pure in heart.
One who is pure in heart is never attracted by the external energy, which urges the individual soul to try to dominate material nature. The pure heart of a devotee is never disturbed when he executes devotional service in the form of hearing, chanting, remembering, etc. In all, there are nine processes one can follow in the execution of devotional service. In any case, a purehearted devotee is never disturbed. The bhakti-yoga process must be carried out by avoiding the ten offenses one can commit while chanting the maha-mantra and the sixty-four offenses one can commit while worshiping the Deity. When a devotee strictly follows the rules and regulations, Bhaktidevi becomes very much satisfied with him, and at that time he is never disturbed by anything external. A devotee is also called a muni. The word muni means “thoughtful.” A devotee is as thoughtful as a nondevotee is speculative. The nondevotee’s speculation is impure, but a devotee’s thoughts are pure. Lord Kapila and Sukadeva Gosvami are also called muni, and Vyasadeva is addressed as Mahamuni. A devotee is addressed as muni, or thoughtful, when he purely understands the Supreme Personality of Godhead. The conclusion is that when one’s heart is purified by the association of devotees and by the avoidance of the offenses committed when chanting and worshiping the Lord, the transcendental name, form and activities of the Lord are revealed by the Lord.