Catur-vidha bhajante mam
Janah sukrtino ‘rjuna
arto jijnasur artharthi
jnani ca bharatarsabha
(Knowledge of the Absolute, Text 16 Chapter 7)
Meaning: O best among the Bharatas, four kinds of pious men begin to render devotional service unto Me-the distressed, the desirer of wealth, the inquisitive, and he who is searching for knowledge of the Absolute.
*** One should render transcendental loving service to the Supreme Lord Krsna favorably and without desire for material profit or gain through fruitive activities or philosophical speculation. That is called pure devotional service.
Bhagavad Gita: Pure devotional Service (Text 16 Chapter 7)]