Srimad Bhagavatam Canto 06, Chapter 01, Text 15

SB 6.1.15

kecit kevalaya bhaktya
agham dhunvanti kartsnyena
 niharam iva bhaskarah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Only a rare person who has adopted complete, unalloyed devotional service to Krsna can uproot the weeds of sinful actions with no possibility that they will revive. He can do this simply by discharging devotional service, just as the sun can immediately dissipate fog by its rays.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
In the previous verse Sukadeva Gosvami gave the example that the dried leaves of creepers beneath a bamboo tree may be completely burnt to ashes by a fire, although the creepers may sprout again because the root is still in the ground. Similarly, because the root of sinful desire is not destroyed in the heart of a person who is cultivating knowledge but who has no taste for devotional service, there is a possibility that his sinful desires will reappear. As stated in Srimad-Bhagavatam (10.14.4):
sreyah-srtim bhaktim udasya te vibho
 klisyanti ye kevala-bodha-labdhaye
Speculators who undergo great labor to gain a meticulous understanding of the material world by distinguishing between sinful and pious activities, but who are not situated in devotional service, are prone to material activities. They may fall down and become implicated in fruitive activities. If one becomes attached to devotional service, however, his desires for material enjoyment are automatically vanquished without separate endeavor. Bhaktih paresanubhavo viraktir anyatra ca: if one is advanced in Krsna consciousness, material activities, both sinful and pious, automatically become distasteful to him. That is the test of Krsna consciousness. Both pious and impious activities are actually due to ignorance because a living entity, as an eternal servant of Krsna, has no need to act for his personal sense gratification. Therefore as soon as one is reclaimed to the platform of devotional service, he relinquishes his attachment for pious and impious activities and is interested only in what will satisfy Krsna. This process of bhakti, devotional service to Krsna (vasudeva-parayana), relieves one from the reactions of all activities.
Since Maharaja Pariksit was a great devotee. the answers of his guru, Sukadeva Gosvami, concerning karma-kanda and jñana-kanda could not satisfy him. Therefore Sukadeva Gosvami, knowing very well the heart of his disciple, explained the transcendental bliss of devotional service. The word kecit, which is used in this verse, means. “a few people but not all.” Not everyone can become Krsna conscious. As Krsna explains in Bhagavad-gita (7.3):
manusyanam sahasresu
 kascid yatati siddhaye
yatatam api siddhanam
 kascin mam vetti tattvatah
“Out of many thousands among men, one may endeavor for perfection, and of those who have achieved perfection, hardly one knows Me in truth.” Practically no one understands Krsna as He is, for Krsna cannot be understood through pious activities or attainment of the most elevated speculative knowledge. Actually the highest knowledge consists of understanding Krsna. Unintelligent men who do not understand Krsna are grossly puffed up, thinking that they are liberated or have themselves become Krsna or Narayana. This is ignorance.
To indicate the purity of bhakti, devotional service, Srila Rupa Gosvami says in Bhakti-rasamrta-sindhu (1.1.11):
anukulyena krsnanu-
 silanam bhaktir uttama
“One should render transcendental loving service to the Supreme Lord Krsna favorably and without desire for material profit or gain through fruitive activities or philosophical speculation. That is called pure devotional service.” Srila Rupa Gosvami further explains that bhakti is klesaghni subhada, which means if one takes to devotional service, all kinds of unnecessary labor and material distress cease entirely and one achieves all good fortune. Bhakti is so powerful that it is also said to be moksa-laghutakrt; in other words, it minimizes the importance of liberation.
Nondevotees must undergo material hardships because they are prone to commit sinful fruitive activities. The desire to commit sinful actions continues in their hearts due to ignorance. These sinful actions are divided into three categories — pataka, maha-pataka and atipataka — and also into two divisions; prarabdha and aprarabdha. Prarabdha refers to sinful reactions from which one is suffering at the present, and aprarabdha refers to sources of potential suffering. When the seeds (bija) of sinful reactions have not yet fructified, the reactions are called aprarabdha. These seeds of sinful action are unseen, but they are unlimited, and no one can trace when they were first planted. Because of prarabdha, sinful reactions that have already fructified, one is seen to have taken birth in a low family or to be suffering from other miseries.
When one takes to devotional service, however, all phases of sinful life, including prarabdha, aprarabdha and bija, are vanquished. In Srimad-Bhagavatam (11.14.19) Lord Krsna tells Uddhava:
yathagnih susamrddharcih
 karoty edhamsi bhasmasat
tatha mad-visaya bhaktir
 uddhavainamsi krtsnasah
“My dear Uddhava, devotional service in relationship with Me is like a blazing fire that can burn to ashes all the fuel of sinful activities supplied to it.” How devotional service vanquishes the reactions of sinful life is explained in Srimad-Bhagavatam (3.33.6) in a verse spoken during Lord Kapiladeva’s instructions to His mother, Devahuti. Devahuti said:
 yat-prahvanad yat-smaranad api kvacit
svado ’pi sadyah savanaya kalpate
 kutah punas te bhagavan nu darsanat
“My dear Lord, if even a person born in a family of dog-eaters hears and repeats the chanting of Your glories, offers respects to You and remembers You, he is immediately greater than a brahmana and is therefore eligible to perform sacrifices. Therefore, what is to be said of one who has seen You directly?”
In the Padma Purana there is a statement that persons whose hearts are always attached to the devotional service of Lord Visnu are immediately released from all the reactions of sinful life. These reactions generally exist in four phases. Some of them are ready to produce results immediately, some are in the form of seeds, some are unmanifested, and some are current. All such reactions are immediately nullified by devotional service. When devotional service is present in one’s heart, desires to perform sinful activities have no place there. Sinful life is due to ignorance, which means forgetfulness of one’s constitutional position as an eternal servant of God, but when one is fully Krsna conscious he realizes that he is God’s eternal servant.
In this regard, Srila Jiva Gosvami comments that bhakti may be divided into two divisions: (1) santata, devotional service that continues incessantly with faith and love, and (2) kadacitki, devotional service that does not continue incessantly but is sometimes awakened. Incessantly flowing devotional service (santata) may also be divided into two categories: (1) service performed with slight attachment and (2) spontaneous devotional service. Intermittent devotional service (kadacitki) may be divided into three categories: (1) ragabhasamayi, devotional service in which one is almost attached, (2) ragabhasa-sunya-svarupa-bhuta, devotional service in which there is no spontaneous love but one likes the constitutional position of serving, and (3) abhasa-rupa, a slight glimpse of devotional service. As for atonement, if one has caught even a slight glimpse of devotional service, all needs to undergo prayascitta, atonement, are superseded. Therefore atonement is certainly unnecessary when one has achieved spontaneous love and, above that, attachment with love, which are signs of increasing advancement in kadacitki. Even in the stage of abhasa-rupa bhakti, all the reactions of sinful life are uprooted and vanquished. Srila Jiva Gosvami expresses the opinion that the word kartsnyena means that even if one has a desire to commit sinful actions, the roots of that desire are vanquished merely by abhasa-rupa bhakti. The example of bhaskara, the sun, is most appropriate. The abhasa feature of bhakti is compared to dawn, and the accumulation of one’s sinful activities is compared to fog. Since fog does not spread throughout the sky, the sun need do no more than merely manifest its first rays, and the fog immediately disappears. Similarly, if one has even a slight relationship with devotional service, all the fog of his sinful life is immediately vanquished.
Srimad Bhagavatam Canto 06, Chapter 01, Text 13-14
Srimad Bhagavatam Canto 06, Chapter 01, Text 16