Contrary to popular beliefs, practices of bhakti-yoga can 
take one to the highest levels of spiritual realization.
Bhakti-yoga Defined


The desire to gratify one’s own senses is kama [lust], but the desire to please the senses of Lord Krsna is prema [love].    
(Cc. Adi 4.165)
Bhakti is not an activity of this material world. It is the activity in relationship with Krsna. Therefore it is not material. It is transcendental.
(Lecture on Bhagavad-gita 1.13–14, London, July 14, 1973)
Anyabhilasita-sunyam  jnana-karmady-anavrtam/ anukulyena krsnanu- silanam bhaktir uttama: “‘When first-class devotional service develops, one must be devoid of all material desires, knowledge obtained by monistic philosophy, and fruitive action. The devotee must constantly serve Krsna favorably, as Krsna desires.’
(Bhakti-rasamrta-sindhu (1.1.11))
Sarvopadhi-vinirmuktam tat-paratvena nirmalam/ hrsikena hrsikesa-sevanam bhaktir ucyate: ” “Bhakti, or devotional service, means engaging all our senses in the service of the Lord, the Supreme Personality of Godhead, the master of all the senses. When the spirit soul renders service unto the Supreme, there are two side effects. One is freed from all material designations, and one’s senses are purified simply by being employed in the service of the Lord.” 
(Bhakti-rasamrta-sindhu (1.1.12))
Bhakti-yoga Versus Other Yogas 
In the astanga-yoga system, the seventh stage of perfection is dhyana. This dhyana is the third stage in devotional service. There are nine stages of devotional service. The first is hearing, and then comes chanting and then contemplating. By executing devotional service, therefore, one automatically becomes an expert jnani and an expert yogi. In other words, jnana and yoga are different preliminary stages of devotional service. 
(Bhagavatam 3.33.26, purport)
The culmination of all kinds of yoga practices lies in bhakti-yoga. All other yogas are but means to come to the point of bhakti in bhakti-yoga. Yoga actually means bhakti-yoga; all other yogas are progressions toward the destination of bhakti-yoga. From the beginning of karma-yoga to the end of bhakti-yoga is a long way to self-realization . . . . Factually, bhakti-yoga is the ultimate goal, but to analyze bhakti-yoga minutely one has to understand these other yogas. 
(Gita 6.47, purport)
Development of Bhakti in One’s Heart
By the mercy of the spiritual master and Krsna one receives the seed of devotional service. Then one has to sow the seed in the field of his heart, just as a gardener sows the seed of a valuable tree. After sowing this seed, one has to water it by chanting and hearing the holy name of the Supreme Lord and by taking part in discussions about the science of devotional service in a society of pure devotees. When the plant of devotional service sprouts up from the seed of devotion, it begins to grow freely. When it is fully grown, it surpasses the length and breadth of this universe and enters the transcendental atmosphere of the spiritual world, where everything is bathed in the effulgence of the brahmajyoti. The plant penetrates even the brahmajyoti and gradually enters the planet known as Goloka Vrindavana. There the plant takes shelter at the lotus feet of Krsna. That is the ultimate goal of devotional service. After attaining this position, the plant produces the fruit of love of Godhead. To taste this fruit, however, it is necessary for the devotee, or transcendental gardener, to water the plant daily by chanting and hearing. Unless one waters the plant by chanting and hearing, there is every chance that it will dry up.
(Teachings of Lord Caitanya, Chapter 1)
Awards Transcendental Happiness

His Divine Grace A.C.Bhaktivedanta Swami Prabhupada

As long as the material body exists, one has to meet the demands of the body, namely eating, sleeping, defending and mating. But a person who is in pure bhakti-yoga, or in Krsna consciousness, does not arouse the senses while meeting the demands of the body. Rather, he accepts the bare necessities of life, making the best use of a bad bargain, and enjoys transcendental happiness in Krsna consciousness.
(Gita 6.20–23, purport)
In the bhakti school, a householder brahmacari is allowed controlled sex life because the cult of bhakti-yoga is so powerful that one automatically loses sexual attraction, being engaged in the superior service of the Lord. 
(Gita 6.13–14, purport)
The Direct Method
The path of bhakti-yoga is especially suitable for this age because it is the most direct method of God realization.    
(Gita 6.37, purport)
Lord Sri Krsna is the fullest manifestation of the Supreme Absolute Truth, and therefore one who is surrendered to the Supreme Person is a successful transcendentalist. To reach this goal of life through Brahman and Paramatma realization takes many, many births (bahunam janmanam ante  [Bg. 7.19]). Therefore the supermost path of transcendental realization is bhakti-yoga, or Krsna consciousness, the direct method. 
(Gita 6.38, purport)
Activities in Bhakti-yoga
Bhakti-yoga is the system that the Gita recommends above all others. Generally, the bhakti-yogis are engaged in five different ways: (1) santa-bhakta, engaged in devotional service in neutrality; (2) dasya-bhakta, engaged in devotional service as servant; (3) sakhya-bhakta, engaged as friend; (4) vatsalya-bhakta, engaged as parent; and (5) madhurya-bhakta, engaged as conjugal lover of the Supreme Lord.
(Gita 8.14, purport)
To practice the regulative principles of bhakti-yoga one should, under the guidance of an expert spiritual master, follow certain principles: one should rise early in the morning, take bath, enter the temple and offer prayers and chant Hare Krsna, then collect flowers to offer to the Deity, cook foodstuffs to offer to the Deity, take prasada, and so on. There are various rules and regulations which one should follow. And one should constantly hear Bhagavad-gita and Srimad-Bhagavatam from pure devotees. This practice can help anyone rise to the level of love of God, and then he is sure of his progress into the spiritual kingdom of God. This practice of bhakti-yoga, under the rules and regulations, with the direction of a spiritual master, will surely bring one to the stage of love of God.
(Gita 12.9, purport)
The Fate of an Unsuccessful Bhakti-Yogi
If the bhakti-yoga system, or Krsna consciousness, is half finished or one-fourth finished, or 10% finished not complete finished then what is the result? Krsna says, svalpam apy asya dharmasya trayate mahato bhayat. Even if it is little understood, it can save him from the greatest danger. And suchinam srimatam gehe yoga-bhrasto ’bhijayate. If one is not successful in this life, then he is given another chance in his next life. Where? Suchinam in the family of a nice transcendentalist, a brahmana or a Vaishnava. Or if he is less qualified, then he may take birth in a rich family. In rich family he has no economic problem, and in a pious family he gets direct opportunity to advance his past Krsna consciousness again.
(Room Conversation, July 16, 1968, Montreal)