SB 6.16.26

śrī-śuka uvāca
bhaktāyaitāṁ prapannāya
 vidyām ādiśya nāradaḥ
yayāv aṅgirasā sākaṁ
 dhāma svāyambhuvaṁ prabho
Word for word: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; bhaktāya — unto the devotee; etām — this; prapannāya — unto one who fully surrendered; vidyām — transcendental knowledge; ādiśya — instructing; nāradaḥ — the great sage Nārada; yayau — left; aṅgirasā — the great saint Aṅgirā; sākam — with; dhāma — for the topmost planet; svāyambhuvam — belonging to Lord Brahmā; prabho — O King.
Translation: 
Śrī Śukadeva Gosvāmī continued: Nārada, having become the spiritual master of Citraketu, instructed him fully in this prayer because Citraketu was fully surrendered. O King Parīkṣit, Nārada then left with the great sage Aṅgirā for the topmost planet, known as Brahmaloka.
Purport: 

When Aṅgirā had first come to visit King Citraketu, he did not bring Nārada with him. However, after the death of Citraketu’s son, Aṅgirā brought Nārada to instruct King Citraketu about bhakti-yoga. The difference was that in the beginning Citraketu was not in a temperament of renunciation, but after the death of his son, when he was overwhelmed by his great plight, he was awakened to the platform of renunciation by instructions regarding the falsity of this material world and material possessions. It is only at this stage that bhakti-yoga can be instructed. As long as one is attached to material enjoyment, bhakti-yoga cannot be understood. This is confirmed in Bhagavad-gītā (2.44):

bhogaiśvarya-prasaktānāṁ
 tayāpahṛta-cetasām
vyavasāyātmikā buddhiḥ
 samādhau na vidhīyate

“In the minds of those who are too attached to sense enjoyment and material opulence, and who are bewildered by such things, the resolute determination of devotional service to the Supreme Lord does not take place.” As long as one is very much attached to material enjoyment, one cannot concentrate his mind on the subject matter of devotional service.

The Kṛṣṇa consciousness movement is progressing successfully in the Western countries at the present moment because the youth in the West have reached the stage of vairāgya, or renunciation. They are practically disgusted with material pleasure from material sources, and this has resulted in a population of hippies throughout the Western countries. Now if these young people are instructed about bhakti-yoga, Kṛṣṇa consciousness, the instructions will certainly be effective.

As soon as Citraketu understood the philosophy of vairāgya-vidyā, the knowledge of renunciation, he could understand the process of bhakti-yoga. In this regard Śrīla Sārvabhauma Bhaṭṭācārya has said, vairāgya-vidyā-nija-bhakti-yoga. Vairāgya-vidyā and bhakti-yoga are parallel lines. One is essential for understanding the other. It is also said, bhaktiḥ pareśānubhavo viraktir anyatra ca (Bhāg. 11.2.42). Advancement in devotional service, or Kṛṣṇa consciousness, is characterized by increasing renunciation of material enjoyment. Nārada Muni is the father of devotional service, and therefore, just to bestow causeless mercy upon King Citraketu, Aṅgirā brought Nārada Muni to instruct the King. These instructions were extremely effective. Anyone who follows in the footsteps of Nārada Muni is certainly a pure devotee.