It is said in Caitanya-caritāmṛta (Madhya 22.38-39):
kṛṣṇa kahe,—'āmā bhaje, māge viṣaya-sukha
amṛta chāḍi' viṣa māge,—ei baḍa mūrkha
āmi—vijña, ei mūrkhe 'viṣaya' kene diba?
sva-caraṇāmṛta diyā 'viṣaya' bhulāiba
"Kṛṣṇa says, 'If one engages in My transcendental loving service but at the same time wants the opulence of material enjoyment, he is very, very foolish. Indeed, he is just like a person who gives up ambrosia to drink poison. Since I am very intelligent, why should I give this fool material prosperity? Instead I shall induce him to take the nectar of the shelter of My lotus feet and make him forget illusory material enjoyment.' " If a devotee maintains some material desire and at the same time very sincerely desires to engage at the lotus feet of Kṛṣṇa, Kṛṣṇa may directly give him unalloyed devotional service and take away all his material desires and possessions. This is the Lord's special favor to devotees. Otherwise, if one takes to Kṛṣṇa's devotional service but still has material desires to fulfill, he may become free from all material desires, as Dhruva Mahārāja did, but this may take some time. However, if a very sincere devotee wants only Kṛṣṇa's lotus feet, Kṛṣṇa directly gives him the position of śuddha-bhakti, unalloyed devotional service.

(Srimad Bhagavatam------8:16:21--------purport).

Śuddha-bhakti, the activity of the soul proper—in other words, engagement in the transcendental loving service of the Lord—is performed in a liberated condition. In Bhagavad-gītā (14.26) it is stated:
māṁ ca yo 'vyabhicāreṇa
bhakti-yogena sevate
sa guṇān samatītyaitān
brahma-bhūyāya kalpate
"One who engages in full devotional service, who does not fall down in any circumstance, at once transcends the modes of material nature and thus comes to the level of Brahman."

Avyabhicāriṇī bhakti means unalloyed devotion. A person engaged in devotional service must be free from material motives. In this Kṛṣṇa consciousness movement, one's consciousness must be changed. If consciousness is aimed toward material enjoyment, it is material consciousness, and if it is aimed toward serving Kṛṣṇa, it is Kṛṣṇa consciousness. A surrendered soul serves Kṛṣṇa without material considerations (anyābhilāṣitā-śūnyam (Bhakti-rasāmṛta-sindhu 1.1.11)). Jñāna-karmādy-anāvṛtam: unalloyed devotional service, which is transcendental to the activities of the body and mind, such as jñāna (mental speculation) and karma (fruitive work), is called pure bhakti-yoga. Bhakti-yoga is the proper activity of the soul, and when one actually engages in unalloyed, uncontaminated devotional service, he is already liberated (sa guṇān samatītyaitān (B.G.14:26).

(Nectar of Instruction).

If one cherishes pure loving devotion to Me, thinking of Me as his son, his friend or his beloved, regarding himself as great and considering Me his equal or inferior, I become subordinate to him."
In the Caitanya-caritāmṛta three kinds of devotional service are described—namely, bhakti (ordinary devotional service), śuddha-bhakti (pure devotional service) and viddha-bhakti (mixed devotional service).

When devotional service is executed with some material purpose, involving fruitive activities, mental speculations or mystic yoga, it is called mixed or adulterated devotional service. Besides bhakti-yoga, the Bhagavad-gītā also describes karma-yoga, jñāna-yoga and dhyāna-yoga. Yoga means linking with the Supreme Lord, which is possible only through devotion. Fruitive activities ending in devotional service, philosophical speculation ending in devotional service, and the practice of mysticism ending in devotional service are known respectively as karma-yoga, jñāna-yoga and dhyāna-yoga. But such devotional service is adulterated by the three kinds of material activities.

(Sri Caitanya Caritamrta-------1:4:21-22--------translation and purport).

For those grossly engaged in identifying the body as the self, pious activity, or karma-yoga, is recommended. For those who identify the mind with the self, philosophical speculation, or jñāna-yoga, is recommended. But devotees standing on the spiritual platform have no need of such material conceptions of adulterated devotion. Adulterated devotional service does not directly aim for love of the Supreme Personality of Godhead. Therefore service performed strictly in conformity with the revealed scriptures is better than such viddha-bhakti because it is free from all kinds of material contamination. It is executed in Kṛṣṇa consciousness, solely to please the Supreme Personality of Godhead.
Those who are spontaneously devoted to the Lord and have no aims for material gain are called attracted devotees. They are spontaneously attracted to the service of the Lord, and they follow in the footsteps of self-realized souls. Their pure devotion (śuddha-bhakti), manifested from pure love of Godhead, surpasses the regulative principles of the authoritative scriptures. Sometimes loving ecstasy transcends regulative principles; such ecstasy, however, is completely on the spiritual platform and cannot be imitated. The regulative principles help ordinary devotees rise to the stage of perfect love of Godhead. Pure love for Kṛṣṇa is the perfection of pure devotion, and pure devotional service is identical with spontaneous devotional service.

Flawless execution of regulative principles is exhibited in the Vaikuṇṭha planets. By strictly executing these principles one can be elevated to the Vaikuṇṭha planets. But spontaneous pure loving service is found in Kṛṣṇaloka alone.

(Sri Caitanya Caritamrta-------1:4:21-22-------- purport).