Yoga aims at controlling the senses. By practice of the mystic process of bodily exercise in sitting, thinking, feeling, willing, concentrating, meditating and at last being merged into transcendence, one can control the senses. The senses are considered like venomous serpents, and the yoga system is just to control them. On the other hand, Nārada Muni recommends another method for controlling the senses in the transcendental loving service of Mukunda, the Personality of Godhead. By his experience he says that devotional service to the Lord is more effective and practical than the system of artificially controlling the senses. In the service of the Lord Mukunda, the senses are transcendentally engaged. Thus there is no chance of their being engaged in sense satisfaction. The senses want some engagement. To check them artificially is no check at all because as soon as there is some opportunity for enjoyment, the serpentlike senses will certainly take advantage of it. There are many such instances in history, just like Viśvāmitra Muni's falling a victim to the beauty of Menakā. But Ṭhākura Haridāsa was allured at midnight by the well-dressed Māyā, and still she could not induce that great devotee into her trap.
The whole idea is that without devotional service of the Lord, neither the yoga system nor dry philosophical speculation can ever become successful. Pure devotional service of the Lord, without being tinged with fruitive work, mystic yoga or speculative philosophy, is the foremost procedure to attain self-realization. Such pure devotional service is transcendental in nature, and the systems of yoga and jñāna are subordinate to such a process. When the transcendental devotional service is mixed with a subordinate process, it is no longer transcendental but is called mixed devotional service.
(Srimad Bhagavatam-1:6:35, purport).

All religious activities are meant ultimately to satisfy the Supreme Personality of Godhead. The Lord is the father of all religious principles. As stated in Bhagavad-gītā (7.16), four kinds of pious men—the needy, the distressed, the enlightened and the inquisitive—approach the Lord in devotional service, and their devotion is mixed with material affection. But above them are the pure devotees, whose devotion is not tainted by any material tinges of fruitive work or speculative knowledge. Those who are only miscreants throughout their lives are compared to demons (Bhagavad-Gita-7:15). They are bereft of all knowledge, in spite of any academic educational career they may pursue. Such miscreants are never candidates for satisfying the Lord.

(Srimad Bhagavatam-3:7:35, purport).

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

After his fourth proposal was rejected, Rāmānanda Rāya said that devotional service rendered without any attempt at cultivation of knowledge or mental speculation is the highest stage of perfection. To support this view, he gave evidence from Śrīmad-Bhāgavatam (10.14.3) wherein Lord Brahmā tells the Supreme Personality of Godhead:
jñāne prayāsam udapāsya namanta eva
jīvanti san-mukharitāṁ bhavadīya-vārtām
sthāne sthitāḥ śruti-gatāṁ tanu-vāṅ-manobhir
ye prāyaśo 'jita jito 'py asi tais tri-lokyām
"My dear Lord, one should give up monistic speculation and the cultivation of knowledge altogether. He should begin his spiritual life in devotional service by receiving information of the Lord's activities from a realized devotee of the Lord. If one cultivates his spiritual life by following these principles and keeping himself on the honest path in life, then although Your Lordship is never conquered, You become conquered by such a process."
When Rāmānanda Rāya presented this proposal, Lord Caitanya at once said, "Yes, this is right." In this age there is no possibility of acquiring spiritual knowledge by renunciation, by mixed devotional service, by fruitive activity in mixed devotional service, or by the culture of knowledge. Because most people are fallen and because there is no time to elevate them by a gradual process, the best course, according to Lord Caitanya, is to let them remain in whatever condition they are in but to engage them in hearing of the activities of the Supreme Lord as those activities are explained in Bhagavad-gītā and Śrīmad-Bhāgavatam. The transcendental messages of the scriptures should be received from the lips of realized souls. In this way a person may continue to live in whatever condition he is in and still make progress in spiritual advancement. Thus one can surely advance and fully realize the Supreme Personality of Godhead.
(Teachings of Lord Caitanya-chapter 28).