By hearing from raganuga-sadhus, greed develops.

“Śrīla Rūpa Gosvāmī has personally given the following definition of lobha (sacred greed) in Śrī Bhakti Rasāmṛta Sindhu: ‘When the heart yearns for the sweetness of the mutual feelings of Kṛṣṇa and His eternal associates in Vraja, and one is not dependent on scriptural injunctions or logical arguments, then that is the definition of ‘the cause of sacred greed’.”
(Srila Vishvanatha Cakravartipada, RVC)

“There are two causes for the appearance of the aforementioned sacred greed: The mercy of God or the mercy of another anurāgī devotee. There are again two kinds of mercy bestowed by a devotee: prāktana and ādhunika. prāktana means mercy bestowed by a rāgānugā bhakta in a previous life, and ādhunika is mercy bestowed in the present birth. The prāktana-devotee takes shelter of the lotus feet of a rāgānugā guru after the sacred greed has arisen in him, the ādhunika will get that sacred greed only after having surrendered to the feet of such a guru. It is said (in Bhakti Rasāmṛta Sindhu): “The only causes of the appearance of sacred greed is the mercy of Kṛṣṇa or His devotee. Therefore some call the path of rāgānugā bhakti also puṣṭi mārga (the path of grace).”
(Srila Vishvanatha Cakravartipada, RVC)

After giving the definition of the cause of sacred greed the blessed author now describes the causes for attaining this greed. Greed for rāgānugā bhajana can only be attained by the grace of Śrī Kṛṣṇa or the grace of the great saints that are themselves passionately attached to the sweet feelings of Śrī Kṛṣṇa’s associates. Kṛṣṇa rarely bestows His mercy on new aspirants, therefore almost always this sacred greed arises by the grace of the aforementioned saints.

There are two kinds of sacred greed that arises by the grace of the saints – prāktana and ādhunikī. Those who have attained lobha by the mercy of rāgānugā saints in previous births will revive the cultivation of that lobha in their present birth and go on with rāgānugā bhajana, taking shelter of the feet of a guru according to their previous lives’ saṁskāra (cultivation), which can be dāsya or sakhya or so. Those who did not cultivate such greed in their previous lives first take shelter of the lotus feet of a guru, and after they hear about the great love of Śrī Kṛṣṇa and His eternal associates the greed awakens within them.
There is no other means than the grace of Śrī Kṛṣṇa and His pure devotees to attain this greed for rāgānugā bhajana, and the blessed author has proven it by quoting a śloka from Bhakti Rasāmṛta Sindhu.

In his commentary on this śloka Śrīmat Jīva Gosvāmīpāda has written: kṛṣṇeti – mātra padasya vidhi mārge kutracit karmādi samarpaṇam api dvāraṁ bhavatīti tad vicchedārthaḥ prayoga iti bhāva. “The word mātra is used in the above śloka ‘kṛṣṇa tad-bhakta kāruṇya mātra lābhaika hetukā’ because sometimes the offering of fruitive activities can lead to entry into vaidhī bhakti, whereas rāgānugā bhakti is only (mātra) attained through grace.” Greed for rāgānugā bhakti is more rarely attained than bhāva or rati in vidhi bhakti, and it is only attainable through grace (Śrī Mukunda Dāsa Gosvāmī). The devotees from the Vallabha Sampradāya call this rāgānugā mārga puṣṭi mārga (the path of grace).
(Srila Ananta das Babaji, tika to RVC)

The sadhaka in whom the greed for raganuga-bhakti has awakened, purifies his heart so that this sacred greed gets thicker, before turning into deep taste (RUCI). Only then can the moonlight of the raga of the eternal associates shine into the heart of the sadhaka.

Lord Kṛṣṇa Himself describes (in Śrīmad Bhāgavata 11.14.26) how the devotee on the path of sacred passion advances and becomes more purified and more obsessed with sacred greed by the day, from the initial stage of surrender to the feet of a guru up to the point in which he directly attains the Lord:

‘The more one’s mind gets purified by hearing and chanting of My beautiful pastimes, the better one is able to discern the subtle reality (of the Self), just as the eye is better able to perceive more and more subtle things when it is treated with medicinal ointment’.
(Srila Vishvanatha Cakravartipada, RVC)

Here we see that the path of raganuga-bhakti starts with “guru-pada-ashraya”, surrendering to Sri Gurudeva who then mercifully makes the sadhaka qualified to serve in raganuga-bhakti by giving him the diksha-mantras and who instructs the sadhaka on the path to perfection.

When the greed of a rāgānugā aspirant leads him down the road of rāga, keeping his beloved object in the centre, then it awakens a special taste for the forms and pastimes of Śrī Kṛṣṇa and His associates. At first the greed of an aspirant will be scattered over many different subject matters and cannot focus on the actual beloved object, but when sādhana bhajana ripens this greed will give up all other subject matters and will focus on the beloved. In this paragraph the blessed author shows how this sacred greed gradually develops.

After the rāgānugīya practitioner has taken shelter of the lotus feet of Śrī Guru the stream of his bhajana starts flowing as he engages in hearing and chanting the glories of the Lord in the company of the devotees. Thus his heart is gradually cleansed from vices like lust and becomes completely immaculate. The purer his heart gets through this cleansing-process, the stronger the sacred greed will get in his heart.
(Srila Ananta das Babaji, tika to RVC)