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.