"In bhakti-yoga it is recommended that a devotee follow nine principles; sravanam kirtanam visnoh smaranam pada-sevanam arcanam vandanam dasyam sakhyam atma-nivedanam. This service of glorifying the Lord by hearing, chanting and so on is not, of course, meant for the benefit of the Lord; this devotional service is recommended for the benefit of the devotee. The Lord is always glorious, whether the devotee glorifies Him or not, but if the devotee engages in glorifying the Lord, the devotee himself automatically becomes glorious. Ceto-darpana-marjanam bhava-maha-davagni-nirvapanam. By glorifying the Lord constantly, the living entity becomes purified in the core of his heart, and thus he can understand that he does not belong to the material world but is a spirit soul whose actual activity is to advance in Krsna consciousness so that he may become free from the material clutches."
Srimad-Bhagavatam 7:9:11 Purport
"Out of many liberated souls, someone may be qualified to know the Personality of Godhead. In the Bhagavad-gita it is also said by the Lord Himself that out of many hundreds of thousands of people, one may try for perfection in human life, and out of many liberated souls, one may know Him as He is. Therefore, the knowledge of the Personality of Godhead may be attained by devotional service only. Rahasyam means devotional service. Lord Krsna instructed Arjuna in the Bhagavad-gita because He found Arjuna to be a devotee and friend. Without such qualifications, one cannot enter into the mystery of the Bhagavad-gita therefore, one cannot understand the Personality of Godhead unless one becomes a devotee and discharges devotional service. This mystery is love of Godhead. Therein lies the main qualification for knowing the mystery of the Personality of Godhead. And to attain the stage of transcendental love of Godhead, regulative principles of devotional service must be followed. The regulative principles are called vidhi-bhakti, or the devotional service of the Lord, and they can be practiced by a neophyte with his present senses. Such regulative principles are mainly based on hearing and chanting of the glories of the Lord. And such hearing and chanting of the glories of the Lord can be made possible in the association of devotees only. Lord Caitanya therefore recommended five main principles for attaining perfection in the devotional service of the Lord. The first is association with devotees (hearing); second is chanting the glories of the Lord; third, hearing Srimad-Bhagavatam from the pure devotee; fourth, residing in a holy place connected with the Lord; and fifth, worshiping the Deity of the Lord with devotion. Such rules and regulations are parts of devotional service.
Srimad-Bhagavatam 2:9:31 Purport
"The word sravana refers to giving aural reception to the holy name and descriptions of the Lord's form, qualities, entourage and pastimes as explained in Srimad-Bhagavatam, Bhagavad-gita and similar authorized scriptures. After aurally receiving such messages, one should memorize these vibrations and repeat them (kirtanam). Smaranam means trying to understand more and more about the Supreme Lord, and pada-sevanam means engaging oneself in serving the lotus feet of the Lord according to the time and circumstances. Arcanam means worshiping Lord Visnu as one does in the temple, and vandanam means offering respectful obeisances. Man-mana bhava mad-bhakto mad-yaji mam namaskuru. Vandanam means namaskuru--offering obeisances or offering prayers. Thinking oneself to be nitya-krsna-dasa, everlastingly a servant of Krsna, is called dasyam, and sakhyam means being a well-wisher of Krsna. Krsna wants everyone to surrender unto Him because everyone is constitutionally His servant. Therefore, as a sincere friend of Krsna, one should preach this philosophy, requesting everyone to surrender unto Krsna. Atma-nivedanam means offering Krsna everything, including one's body, mind, intelligence and whatever one may possess. One's sincere endeavor to perform these nine processes of devotional service is technically called bhakti.
Srimad-Bhagavatam 7:5:23-24 Purport
"As stated in Srimad-Bhagavatam (7.5.23), there are nine kinds of devotional service: hearing (sravanam), chanting (kirtanam), remembering (visnoh smaranam), serving (pada-sevanam), worship of the Deity (arcanam), praying (vandanam), carrying out orders (dasyam), serving Him as a friend (sakhyam) and sacrificing everything for the Lord (atma-nivedanam). Although each process appears distinct, when one is situated on the absolute platform he can see that they are identical. For instance, hearing is as good as chanting, and remembering is as good as chanting or hearing. Similarly, engaging in Deity worship is as good as chanting, hearing or remembering. The devotee is expected to accept all nine processes of devotional service, but even if only one process is properly executed, he can still attain the highest position (paramahamsa) and go back home, back to Godhead.
Caitanya-caritamrta, Madyam lila 4:125
"These are the activities of hearing, chanting, remembering, serving, worshiping, praying, obeying, maintaining friendship and surrendering everything. As far as chanting the holy name of Krsna is concerned, one can be freed from all sinful reactions by chanting the holy name without committing offenses. If one chants offenselessly, he may be saved from all sinful reactions. It is very important in devotional service to chant the holy name of the Lord without committing offenses. The nine devotional processes such as sravana and kirtana can all be attained at once if one simply chants the holy name of the Lord offenselessly.
In this regard, Srila Jiva Gosvami states in his book Bhakti-sandarbha (173): yadyapi anya bhaktih kalau kartavya, tada kirtanakhya-bhakti-samyogenaiva. Out of the nine processes of devotional service, kirtana is very important. Srila Jiva Gosvami therefore instructs that the other processes, such as arcana, vandana, dasya and sakhya, should be executed, but they must be preceded and followed by kirtana, the chanting of the holy name. We have therefore introduced this system in all of our centers. Arcana, arati, bhoga offering, Deity dressing and decoration are all preceded and followed by the chanting of the holy name of the Lord - Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare. Hare Rama, Hare Rama, Rama Rama, Hare Hare.
Caitanya-caritamrta, Madyam lila 15:107
"If you have no time to hear, to go to the temple or to hear the speeches of the acaryas, at home you can simply remember the Lord. This Radha-Krsna murti, if you simply remember, meditate, that will also do. Smaranam pada-sevanam. Pada-sevanam means to serve, giving service, rendering service to the lotus feet of the Lord, just like devotees do. They bring flowers, tulasi, and offer to the lotus feet of the Lord. The worshiping of the Lord begins from the leg, from the lotus feet, not directly to the head. That is the way. So pada-sevanam. Then arcanam. Arcanam means the offering aratrika, offering bhoga, cleansing the Deity room and dressing the Lord, changing the flowers. These are called arcanam. Vandanam. If you cannot do this, then offer prayers. Just like in Christian church they offers prayers. That is also bhakti, devotional service. The Muslims, they offer prayers. Any way. Sravanam kirtanam visnoh smaranam pada-sevanam, arcanam vandanam. Vandanam means offering prayer. Dasyam. Dasyam means to work as menial servant of the Lord. Dasyam. Sakhyam, to make friendship with the Lord, just like Arjuna did. He treated Krsna as his friend, and by making friendship with Krsna he became liberated. Sakhyam. And atma-nivedanam. Atma-nivedanam means giving everything to the Lord, even his body, wealth, and everything, just like Bali Maharaja did. So,
Srila Prabhupada Lecture on Srimad-Bhagavatam, 09-08-71, London
"King Malayadhvaja was a great devotee, and after he married the daughter of King Vidarbha, he gave her one nice daughter, whose eyes were black. Figuratively this means that the daughter of King Malayadhvaja was also bestowed with devotional service, for her eyes were always fixed on Krsna. A devotee has no vision in his life other than Krsna. The seven sons are the seven processes of devotional service--hearing, chanting, remembering, offering worship, offering prayers, rendering transcendental loving service and serving the lotus feet of the Lord. Of the nine types of devotional service, only seven were immediately given. The balance--friendship and surrendering everything--were to be developed later. In other words, devotional service is divided into two categories--namely vidhi-marga and raga-marga. The process of becoming friends with the Lord and sacrificing everything for Him belongs to the category of raga-marga, the stage of developed devotional service. For the neophyte, the important processes are those of hearing and chanting (sravanam kirtanam), remembering Krsna, worshiping the Deity in the temple, offering prayers and always engaging in the service of the Lord, and worshiping the lotus feet of the Lord.
The word yaviyasah indicates that these processes are very powerful. After a devotee engages in the processes of sravanam kirtanam visnoh smaranam pada-sevanam. arcanam vandanam dasyam, and is able to secure these processes, he can later become a devotee capable of rendering spontaneous devotional service--namely sakhyam and atma-nivedanam.
Srimad-Bhagavatam 4:28:30 Purport
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.