Prabhupāda: This Kṛṣṇa consciousness movement is training people how to become unalloyed servant of Kṛṣṇa. Śuddha-bhakta, unalloyed, without any adulteration. What is that adulteration?
śīlanaṁ bhaktir uttamā
No other desire. Not that "By worshiping Kṛṣṇa or acting devotional service I shall get this opportunity, this facility," material or spiritual. A real devotee, he does not aspire even for liberation. He doesn't want. He simply wants, "My Lord Kṛṣṇa, wherever I may be, it doesn't matter. Please keep me always engaged in Your consciousness." That's all.
A devotee never aspires that he'll be elevated to the spiritual sky or Vaikuṇṭha or... Never mind. "For thousands and thousands of births I may rot into the hell, but simply I want my Lord, that wherever I may be situated, I may not forget You." Mama janmani janmanīśvare bhavatād bhaktir ahaitukī (Siksastaka 4). Lord Caitanya teaches this. Janmani janmani. Where there is janmani janmani, that means that is not liberation. As soon as you're liberated, you are not supposed to take birth again. But Caitanya Mahāprabhu says, janmani janmani. He doesn't aspire about liberation. "Birth after birth, please keep Me engaged in Your devotional service." That is pure devotion. Ānukūlyena kṛṣṇānu-śīlanaṁ bhaktir uttamā.
So this Kṛṣṇa consciousness movement is meant for purifying the existence of the living entity and engage him constantly in the service of the Lord, and thus he achieves all success of life.
(Srila Prabhupada Lecture, London, September 16, 1969)