As stated in Śrīmad-Bhāgavatam (5.6.18), muktiṁ dadāti karhicit. Śrīla Śukadeva Gosvāmī told Mahārāja Parīkṣit that Kṛṣṇa readily grants liberation but does not very readily grant perfection in devotional service. This means that Kṛṣṇa wants to see that a devotee is actually sincere and serious and that he does not have ulterior motives. If this is the case, devotional service can very easily be successful; otherwise it is very difficult to obtain from the Supreme Personality of Godhead. This verse appears in the Bhakti-rasāmṛta-sindhu(1.1.35).
(Sri Caitanya Caritamrta-----2:24:172-----purport).

"One who engages in full devotional service, unfailing in all circumstances, at once transcends the modes of material nature and thus comes to the level of Brahman." In material consciousness, however, even one who is situated in the mode of goodness is susceptible to pollution by the modes of passion and ignorance. When the mode of goodness is mixed with the mode of passion, one worships the sun-god, Vivasvān. When the mode of goodness is mixed with the mode of ignorance, one worships Gaṇapati, or Gaṇeśa. When the mode of passion is mixed with the mode of ignorance, one worships Durgā, or Kālī, the external potency. When one is simply in the mode of ignorance, one becomes a devotee of Lord Śiva because Lord Śiva is the predominating deity of the mode of ignorance within this material world. However, when one is completely free from the influence of all the modes of material nature, one becomes a pure Vaiṣṇava on the devotional platform. As Śrīla Rūpa Gosvāmī states in the Bhakti-rasāmṛta-sindhu:
anyābhilāṣitā-śūnyaṁ jñāna-karmādy-anāvṛtam
ānukūlyena kṛṣṇānuśīlanaṁ bhaktir uttamā
(CC.2:19:167)
"One should render transcendental loving service to the Supreme Lord Kṛṣṇa favorably and without desire for material profit or gain through fruitive activities or philosophical speculation. That is called pure devotional service."

(Sri Caitanya Caritamrta-----2:24:330-----purport).

"In the beginning one must have a preliminary desire for self-realization. This will bring one to the stage of trying to associate with persons who are spiritually elevated. In the next stage, one becomes initiated by an elevated spiritual master, and under his instruction the neophyte devotee begins the process of devotional service. By execution of devotional service under the guidance of the spiritual master, one becomes freed from all material attachments, attains steadiness in self-realization and acquires a taste for hearing about the Absolute Personality of Godhead, Śrī Kṛṣṇa." (Bhakti-rasāmṛta-sindhu 1.4.15) If one is actually executing devotional service, then anarthas, the unwanted things associated with material enjoyment, will automatically disappear.

(Sri Caitanya Caritamrta-----3:3:251-----purport).

Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura quotes the following definition of rasābhāsa from the Bhakti-rasāmṛta-sindhu (Uttara-vibhāga, Ninth Wave, 1–3, 33, 38 and 41):
pūrvam evānuśiṣṭena vikalā rasa-lakṣaṇā
rasā eva rasābhāsā rasajñair anukīrtitāḥ
syus tridhoparasāś cānurasāś cāparasāś ca te
uttamā madhyamāḥ proktāḥ kaniṣṭhāś cety amī kramāt
prāptaiḥ sthāyi-vibhāvānubhāvādyais tu virūpatām
śāntādayo rasā eva dvādaśoparasā matāḥ
bhaktādibhir vibhāvādyaiḥ kṛṣṇa-sambandha-varjitaiḥ
rasā hāsyādayaḥ sapta śāntaś cānurasā matāḥ
kṛṣṇa-tat-pratipakṣaś ced viṣayāśrayatāṁ gatāḥ
hāsādīnāṁ tadā te ‘tra prājñair aparasā matāḥ
bhāvāḥ sarve tadābhāsā rasābhāsāś ca kecana
amī prokta-rasābhijñaiḥ sarve ‘pi rasanād rasāḥ
“A mellow temporarily appearing transcendental but contradicting mellows previously stated and lacking some of a mellow's necessities is called rasābhāsa, an overlapping mellow, by advanced devotees who know how to taste transcendental mellows. Such mellows are called uparasa (submellows), anurasa (imitation transcendental mellows) and aparasa (opposing transcendental mellows). Thus the overlapping of transcendental mellows is described as being first grade, second grade or third grade. When the twelve mellows—such as neutrality, servitorship and friendship—are characterized by adverse sthāyi-bhāva, vibhāva and anubhāva ecstasies, they are known as uparasa, submellows. When the seven indirect transcendental mellows and the dried-up mellow of neutrality are produced by devotees and moods not directly related to Kṛṣṇa and devotional service in ecstatic love, they are described as anurasa, imitation mellows. If Kṛṣṇa and the enemies who harbor feelings of opposition toward Him are respectively the object and abodes of the mellow of laughter, the resulting feelings are called aparasa, opposing mellows. Experts in distinguishing one mellow from another sometimes accept some overlapping transcendental mellows (rasābhāsa) as rasas due to their being pleasurable and tasteful.” Śrīla Viśvanātha Cakravartī Ṭhākura says, paraspara-vairayor yadi yogas tadā rasābhāsaḥ: "When two opposing transcendental mellows overlap, they produce rasābhāsa, or an overlapping of transcendental mellows."

(Sri Caitanya Caritamrta-----3:5:97-----purport).

As stated by Śrīla Bhaktivinoda Ṭhākura in his Amṛta-pravāha-bhāṣya, some people, usually very rich men, dress like Vaiṣṇavas and give charity to brāhmaṇas. They are also attached to Deity worship, but because of their attachment to material enjoyment, they cannot be pure Vaiṣṇavas. Anyābhilāṣitā-śūnyaṁ jñāna-karmādy-anāvṛtam (Bhakti-rasāmṛta-sindhu 1.1.11). The pure Vaiṣṇava has no desire for material enjoyment. That is the basic qualification of a pure Vaiṣṇava. There are men, especially rich men, who regularly worship the Deity, give charity to brāhmaṇas and are pious in every respect, but they cannot be pure Vaiṣṇavas. Despite their outward show of Vaiṣṇavism and charity, their inner desire is to enjoy a higher standard of material life. Raghunātha dāsa's father, Govardhana, and uncle, Hiraṇya dāsa, were both very charitable to brāhmaṇas. Indeed, the brāhmaṇas from the Gauḍīya district were practically dependent upon them. Thus they were accepted as very pious gentlemen. However, they presented themselves as Vaiṣṇavas to the eyes of people in general, although from a purely spiritual point of view they were ordinary human beings, not pure Vaiṣṇavas. Actual Vaiṣṇavas considered them almost Vaiṣṇavas, not pure Vaiṣṇavas. In other words, they were kaniṣṭha-adhikārīs, for they were ignorant of higher Vaiṣṇava regulative principles. Nevertheless, they could not be called viṣayīs, or blind materialistic enjoyers.

(Sri Caitanya Caritamrta-----3:6:198-----purport).

A materialist does not actually know why one should become a devotee. A devotee's only concern is to satisfy the Supreme Personality of Godhead. Pure devotional service is defined by Śrīla Rūpa Gosvāmī:
anyābhilāṣitā-śūnyaṁ jñāna-karmādy-anāvṛtam
ānukūlyena kṛṣṇānuśīlanaṁ bhaktir uttamā
(Bhakti-rasāmṛta-sindhu 1.1.11)
One should be completely free from all material desires and should serve Kṛṣṇa simply to please Him. When people become interested in their own sense gratification (bhukti-mukti-siddhi-kāmī), some of them desire to enjoy the material world to the fullest extent, some of them desire to be liberated and merge into the existence of Brahman, and others want to perform magic through mystic power and thus become incarnations of God. These are all against the principles of devotional service. One must be free from all material desires. The desire of the impersonalist to merge into the existence of Brahman is also material because such an impersonalist wants to gratify his senses by merging into the existence of Kṛṣṇa instead of serving His lotus feet. Even if such a person merges into the Brahman effulgence, he falls down again into material existence.

(Sri Caitanya Caritamrta-----3:9:68-----purport).

"One who cannot deliver his dependent from the path of birth and death should never become a spiritual master, a relative, a father or mother, or a worshipable demigod, nor should such a person become a husband." Everyone naturally gets a father and mother at the time of birth, but the real father and mother are those who can release their offspring from the clutches of imminent death. This is possible only for parents advanced in Kṛṣṇa consciousness. Therefore any parents who cannot enlighten their offspring in Kṛṣṇa consciousness cannot be accepted as a real father and mother. The following verse from the Bhakti-rasāmṛta-sindhu (1.2.200) confirms the uselessness of serving ordinary parents:
laukikī vaidikī vāpi yā kriyā kriyate mune
hari-sevānukūlaiva sa kāryā bhaktim icchatā
"One should perform only those activities—either worldly or prescribed by Vedic rules and regulations—which are favorable for the cultivation of Kṛṣṇa consciousness."

(Sri Caitanya Caritamrta-----3:13:113-----purport).