Pure devotional service must be freed from all desires for sense gratification, fruitive aspirations and culture of monistic knowledge. One must be freed from all kinds of designations, and when one is thus converted to transcendental purity, one can then serve the Lord by purified senses.
As long as there is the desire to enjoy sensually or to become one with the Supreme or to possess the mystic powers, there is no question of attaining the stage of pure devotional service.
Devotional service is conducted under two categories, namely primary practice and spontaneous emotion. When one can rise to the platform of spontaneous emotion, he can make further progress by spiritual attachment, feeling, love, and many higher stages of devotional life for which there are no English words. We have tried to explain the science of devotional service in our book (The Nectar of Devotion), based on the authority of Bhakti-rasāmṛta-sindhu by Śrīla Rūpa Gosvāmī.
Transcendental devotional service has five stages of reciprocation:
1. The self-realization stage just after liberation from material bondage is called the śānta, or neutral stage.
2. After that, when there is development of transcendental knowledge of the Lord's internal opulences, the devotee engages himself in the dāsya stage.
3. By further development of the dāsya stage, a respectful fraternity with the Lord develops, and above that a feeling of friendship on equal terms becomes manifest. Both these stages are called sākhya stage, or devotional service in friendship.
4. Above this is the stage of paternal affection toward the Lord, and this is called the vātsalya stage.
5. And above this is the stage of conjugal love, and this stage is called the highest stage of love of God, although there is no difference in quality in any of the above stages. The last stage of conjugal love of God is called the mādhurya stage.