SB 4.23.9

sanat-kumāro bhagavān
 yad āhādhyātmikaṁ param
yogaṁ tenaiva puruṣam
 abhajat puruṣarṣabhaḥ
Word for word: 
sanat-kumāraḥ — Sanat-kumāra; bhagavān — most powerful; yat — that which; āha — said; ādhyātmikam — spiritual advancement of life; param — ultimate; yogam — mysticism; tena — by that; eva — certainly; puruṣam — the Supreme Person; abhajat — worshiped; puruṣa-ṛṣabhaḥ — the best of human beings.
Translation: 
Thus the best amongst human beings, Mahārāja Pṛthu, followed that path of spiritual advancement which was advised by Sanat-kumāra. That is to say, he worshiped the Supreme Personality of Godhead, Kṛṣṇa.
Purport: 

In this verse it is clearly said that Mahārāja Pṛthu, practicing the prāṇāyāma-yoga system, engaged in the service of the Supreme Personality of Godhead as advised by the saint Sanat-kumāra. In this verse the words puruṣam abhajat puruṣarṣabhaḥ are significant. Puruṣarṣabha refers to Mahārāja Pṛthu, the best amongst human beings, and puruṣam refers to the Supreme Personality of Godhead. The conclusion is that the best man amongst all men engages in the service of the Supreme Person. One puruṣa is worshipable, and the other puruṣa is the worshiper. When the puruṣa who worships, the living entity, thinks of becoming one with the Supreme Person, he simply becomes bewildered and falls into the darkness of ignorance. As stated by Lord Kṛṣṇa in Bhagavad-gītā (2.12), all living entities assembled in the battlefield, as well as Kṛṣṇa Himself, were also present in the past as individuals and would continue to be present in the future as individuals also. Therefore the two puruṣas, the living entity and the Supreme Personality of Godhead, never lose their respective identities.

Actually, one who is self-realized engages himself in the service of the Lord perpetually, both in this life and in the next. Indeed, for devotees there is no difference between this life and the next. In this life a neophyte devotee is trained to serve the Supreme Personality of Godhead, and in the next life he approaches that Supreme Person in Vaikuṇṭha and renders the same devotional service. Even for the neophyte devotee, devotional service is considered brahma-bhūyāya kalpate. Devotional service to the Lord is never considered a material activity. Since he is acting on the brahma-bhūta platform, a devotee is already liberated. He therefore has no need to practice any other type of yoga in order to approach the brahma-bhūta stage. If the devotee adheres strictly to the orders of the spiritual master, follows the rules and regulations and chants the Hare Kṛṣṇa mantra, it should be concluded that he is already at the brahma-bhūta stage, as confirmed in Bhagavad-gītā (14.26):

māṁ ca yo ’vyabhicāreṇa
 bhakti-yogena sevate
sa guṇān samatītyaitān
 brahma-bhūyāya kalpate

“One who is engaged in full devotional service, unfailing in all circumstances, at once transcends the modes of material nature and thus comes to the level of Brahman.”