It can be concluded that a person who is freed from the bodily concept of life is an eligible candidate for pure devotional service. It is also confirmed in the Bhagavad-gītā that after Brahman realization, when one is freed from material anxieties and can see every living entity on an equal level, he is eligible to enter into devotional service.
As stated before, there are three kinds of happiness-material, spiritual and devotional. Devotional service and the happiness due to its execution are not possible as long as one is materially affected. If someone has desire for material enjoyment or for becoming one with the Supreme, these are both considered material concepts. Because the impersonalists cannot appreciate the spiritual happiness of association and the exchange of loving affairs with the Supreme Personality of Godhead, their ultimate goal is to become one with the Lord. This concept is simply an extension of the material idea. In the material world, everyone is trying to be the topmost head man among all his fellow men or neighbors. Either communally, socially or nationally, everyone is competing to be greater than all others, in the material concept of life. This greatness can be extended to the unlimited, so that one actually wants to become one with the greatest of all, the Supreme Lord. This is also a material concept, although maybe a little more advanced.
However, the perfect spiritual concept of life is complete knowledge of one's constitutional position, in which one knows enough to dovetail himself in the transcendental loving service of the Lord. One must know that he is finite and that the Lord is infinite. Thus it is not possible to actually become one with the Lord even if one aspires for this. It is simply not possible. Therefore, anyone who has any desire or aspiration for satisfying his senses by becoming more and more important, either in the material sense or in the spiritual sense, cannot actually relish the really sweet taste of devotional service. Śrīla Rūpa Gosvāmī has therefore compared possessing these bhukti (material) and mukti (liberation) desires with being influenced by the black art of a witch: in both cases one is in trouble. Bhukti means material enjoyment, and mukti means to become freed from material anxiety and to become one with the Lord. These desires are compared to being haunted by ghosts and witches, because while these aspirations for material enjoyment or spiritual oneness with the Supreme remain, no one can relish the actual transcendental taste of devotional service.
A pure devotee never cares for liberation. Lord Caitanya Mahāprabhu prayed to Kṛṣṇa, "My dear son of Nanda, I do not want any material happiness in the shape of many followers, nor immense opulence in wealth, nor any beautiful wife, nor do I want cessation from material existence. I may take birth many times, one after another, but what I pray from You is that my devotion unto You may always remain unflinching."