“Where does such spiritual greed come from? Rupa Gosvamin summarizes this in Bhakti-rasamrita-sindhu:

When one has gained some perception, from hearing the Bhagavata Purana or other books on the Lord’s sports written by rapturous devotees, that all of Krishna’s senses are pleased by the feelings, beauty and qualities of the residents of Vraja such as Nanda and Yasoda, an attitude arises that is indifferent to scripture or argument and is a symptom of the development of eagerness or greed (lobha). This attitude is, more specifically, the innate, spontaneous desire for the sweetness of those various moods:
“May I also have the same kinds of feelings and qualities.”

Even though spontaneous attraction to the mood of the residents of Vrindavan is so natural, not all persons develop it instantly upon first hearing about it.
The Caitanya-caritamrita says: “Some rare fortunate soul develops greed on hearing the glories of the residents of Vrindavan.”

One needs the mercy of a devotee who is himself endowed with this spirit and the candidate must be possessed of certain qualities on his own—a certain lucidity or clearness of mind—before such greed can appear. Therefore, Rupa says in Bhakti-rasamrita-sindhu (1.2.309) that it is kripaikalabhya, “only available through the mercy of the Lord and his devotees.”

In the Bhakti-sandarbha (“Treatise on Devotion”), Sri Jiva describes the development of greed in the following way:

A devotee whose heart is clear like a crystal will find that when the rays of the moon-like devotion of the residents of Vraja fall upon it, it lights up and takes on that glow itself, i.e., eagerness manifests itself in his heart. Then a curiosity about the dealings or feelings or passions of the eternally perfect residents of Vraja such as Nanda, Yasoda, etc., arises in the practitioner. In other words a desire to know more about the patterns of their feelings occurs and he develops a taste or hunger for those patterns.

The candidate who is qualified for practicing devotion in pursuit of erotic passion (kamanuga bhakti) is further described in Rupa Gosvamin’s Bhakti-rasamrita-sindhu:

Those who have seen the beauty of the image of the Lord or who have heard about his sports with his lovers, from their “falling in love” (purva-raga) to the ecstasies of the circle dance, and who have become eager for the feelings of either the heroines or their friends are qualified for the practice of one of the two types of this form of devotion.28

Sri Jiva’s commentary on this verse is as follows:

Previously [in verse 1.2.292], only the process of hearing was mentioned. Now it appears that it is necessary to see Krishna’s form also. Seeing Krishna’s images, certainly, is also dependent on hearing, for without hearing, there is no possibility that the Lord’s beauty or activities will spring into reality. Moreover, even without seeing the image of the Lord, hearing of his sports will be effective.
Who then is not qualified? Expanding on the verse from Bhakti-rasamrita-sindhu (3.5.2), which was quoted above (page xx), Vishnu Dasa writes in his commentary on Ujjvala-nilamani (1.2):

1) This spiritual discussion is unedifying for those who, though they are devotees of Krishna, have no inclination toward erotic sacred rapture and for those who, considering the Lord’s erotic dalliances to be the same as mundane sexuality, feel dispassion or lack any taste for them.

2) Although there are many devotees in erotic sacred rapture, still, because they have not been properly trained or purified, not all of them are proficient at tasting rapture. For them, this discussion is difficult to grasp.

3) It is improper to discuss this topic before those whose minds are deeply absorbed in the path of injunctions, who, because of having various tendencies, are by nature unaware of the path of passion. The superiority of the path of passion means, after all, that there are unlimited lesser natures unsuited for it.

This conception of the manjari is as difficult to comprehend as it is rare. Yet, as it is extremely important we have no other recourse than that of familiarizing ourselves with it. Although such a task is beyond the capabilities of an uneducated, foolish and most unqualified person such as myself, still, because of the indomitable influence of this holy land and of the blessings of the Vaishnavas, who are all embodiments of Srimati Radharani’s compassion, I have been inspired to take up this task with enthusiasm.

(Sri Kunjabihari das Babaji – Manjari Svarupa Nirupana, introduction)