"I am writing books. I am not being forced by anyone. Everyone can do that. Why one does not do it? Why I get up at night, one o'clock, and do this job? Because I cannot do without it. How one will do it artificially? This is quality. Therefore they like my purports. That quality is shown by Caitanya Mahāprabhu. Śunyayitaṁ jagat sarvaṁ govinda virahena me (Śikṣāṣṭaka 7): 'Oh, I do not see Govinda. The whole world is vacant.' Śunyayitaṁ jagat sarvaṁ govinda virahena me. This is quality. Just like we have got practical example: one man's beloved has died, and he is seeing the whole universe vacant. Is it vacant? So that is quality of love.
So there is no formula of quality. It is to be understood by himself. Just like if after eating something you feel refreshed and get strength, that is quality. You haven't got to take certificate: 'Will you give me a certificate that I have eaten?' You'll understand whether you eaten or not. That is quality. When you'll feel so much ecstasy in chanting Hare Kṛṣṇa, that is quality. Not artificially—'Chant. Chant. Otherwise get out.' This is not quality. This is in expectation that someday you may come to quality. That requires time. That requires sincerity. But quality is there. Śravanādi śuddha citte karaye... (CC Madhya 22.107). It will be awakened. Not by force. Just like love between two person, it cannot be forced: 'You must love him. You must love her.' No, that is no love. That is not love. When they automatically love one another, that is quality."
(Srila Prabhupada Morning Walk, Nairobi, November 2, 1975)