'śuddha-bhakti' haite haya 'premā' utpanna
ataeva śuddha-bhaktira kahiye 'lakṣaṇa'
śuddha-bhakti - pure devotional service without material contaminations; haite - from; haya - is; premā - love of the Supreme Personality of Godhead; utpanna - produced; ataeva - therefore; śuddha-bhaktira - of pure devotional service; kahiye - let me explain; lakṣaṇa - the symptoms.
In the Bhagavad-gītā (18.55) it is said, bhaktyā mām abhijānāti yāvān yaś cāsmi tattvataḥ. One cannot understand the Supreme Personality of Godhead in truth unless he takes to devotional service.