SB 7.13.22
yasya narayano devo
bhagavan hrd-gatah sada
bhaktya kevalayajñanam
dhunoti dhvantam arkavat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Narayana, the Supreme Personality of Godhead, who is full of all opulences, is predominant within the core of your heart because of your being a pure devotee. He always drives away all the darkness of ignorance, as the sun drives away the darkness of the universe.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The words bhaktya kevalaya indicate that simply by executing devotional service one can become full of all knowledge. Krsna is the master of all knowledge (aisvaryasya samagrasya viryasya yasasah sriyah). The Lord is situated in everyone’s heart (isvarah sarva-bhutanam hrd-dese ’rjuna tisthati), and when the Lord is pleased with a devotee, the Lord instructs him. Only to the devotees, however, does the Lord give instructions by which to advance further and further in devotional service. To others, the nondevotees, the Lord gives instructions according to the manner of their surrender. The pure devotee is described by the words bhaktya kevalaya. Srila Visvanatha Cakravarti Thakura explains that bhaktya kevalaya means jñana-karmady-amisraya, “unmixed with fruitive activities or speculative knowledge.” Simply surrendering at the lotus feet is the cause of all a devotee’s enlightenment and awareness.