King Pṛthu's activities took place in Satya-yuga, and in this age this practice of yoga is misunderstood by fallen souls who are not capable of practicing anything. Consequently the śāstras enjoin: kalau nāsty eva nāsty eva nāsty eva gatir anyathā. The conclusion is that unless the karmīs, jñānīs and yogīs come to the point of devotional service to Lord Kṛṣṇa, their so-called austerities and yoga have no value. Nārādhitaḥ: if Hari, the Supreme Personality of Godhead, is not worshiped, there is no point in practicing meditational yoga, performing karma-yoga or culturing empiric knowledge. As far as prāṇāyāma is concerned, chanting of the holy name of the Lord and dancing in ecstasy are also considered prāṇāyāma. In a previous verse, Sanat-kumāra instructed Mahārāja Pṛthu to engage constantly in the service of the Supreme Lord, Vāsudeva.
(Srimad Bhagavatam----4:23:8----purport).

According to the calculations of the demigods, one day (twelve hours) is equal to six months on earth. A hundred years of the demigods would equal thirty-six thousand earth years. Thus King Malayadhvaja executed austerities and penances for thirty-six thousand years. After this time, he became fixed in the devotional service of the Lord. To live on earth for so many years, one has to take birth many times. This confirms the conclusion of Kṛṣṇa. To come to the conclusion of Kṛṣṇa consciousness and remain fixed in the realization that Kṛṣṇa is everything, as well as render service unto Kṛṣṇa, are characteristics of the perfectional stage. As said in Caitanya-caritāmṛta (cc.2:22:62): kṛṣṇe bhakti kaile sarva-karma kṛta haya. When one comes to the conclusion that Kṛṣṇa is everything by worshiping or by rendering devotional service unto Kṛṣṇa, one actually becomes perfect in all respects. Not only must one come to the conclusion that Kṛṣṇa is everything, but he must remain fixed in this realization. This is the highest perfection of life, and it is this perfection that King Malayadhvaja attained at the end.
(Srimad Bhagavatam----4:28:39----purport).

Another symptom is viśoka, which indicates that he is callous to material distress and happiness. Another is vijighatsa, which indicates that he no longer desires material enjoyment. Another symptom is apipātā, which means that he has no desire other than to engage in the devotional service of Kṛṣṇa, his dearmost pursuable Lord. A further symptom is satya-kāma, which indicates that all his desires are directed to the Supreme Truth, Kṛṣṇa. He does not want anything else. He is satya-saṅkalpa. Whatever he desires is fulfilled by the grace of Kṛṣṇa. First of all, he does not desire anything for his material benefit, and secondly if he desires anything at all, he simply desires to serve the Supreme Lord. That desire is fulfilled by the Lord's grace. That is called satya-saṅkalpa. Śrīla Viśvanātha Cakravartī points out that the word mahimā means returning to the spiritual world, back home, back to Vaikuṇṭha.
(Srimad Bhagavatam----5:4:5----purport).

"One should render transcendental loving service to the Supreme Lord Kṛṣṇa favorably and without desire for material profit or gain through fruitive activities or philosophical speculation. That is called pure devotional service." Those who fully engage in devotional service to Kṛṣṇa just to please Him are not interested in the three divisions of heavenly places, namely, divya-svarga, bhauma-svarga and bila-svarga.
(Srimad Bhagavatam----5:17:11----purport).

"Devotees always engaged in the service of the toes of the Lord's lotus feet can very easily become free from hard-knotted desires for fruitive activities. Because this is very difficult, the nondevotees—the jñānīs and yogīs—cannot stop the waves of sense gratification, although they try to do so. Therefore you are advised to engage in the devotional service of Kṛṣṇa, the son of Vasudeva."
Every living being within this material world has a strong desire to enjoy matter to his fullest satisfaction. For this purpose, the conditioned soul must accept one body after another, and thus his strongly fixed fruitive desires continue. One cannot stop the repetition of birth and death without being completely desireless.
(Srimad Bhagavatam----5:18:8----purport).

Bhaktiḥ pareśānubhavo viraktir anyatra ca: (S.B.11:2:42) if one is advanced in Kṛṣṇa consciousness, material activities, both sinful and pious, automatically become distasteful to him. That is the test of Kṛṣṇa consciousness. Both pious and impious activities are actually due to ignorance because a living entity, as an eternal servant of Kṛṣṇa, 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 Kṛṣṇa. This process of bhakti, devotional service to Kṛṣṇa (vāsudeva-parāyaṇa), relieves one from the reactions of all activities.
Since Mahārāja Parīkṣit was a great devotee. the answers of his guru, Śukadeva Gosvāmī, concerning karma-kāṇḍa and jñāna-kāṇḍa could not satisfy him. Therefore Śukadeva Gosvāmī, knowing very well the heart of his disciple, explained the transcendental bliss of devotional service.
(Srimad Bhagavatam----6:1:15----purport).

Śrīla Viśvanātha Cakravartī Ṭhākura has very nicely explained the word bhayena, which means "by fear." When the gopīs went to Kṛṣṇa in the dead of night, they certainly feared chastisement by their relatives—their husbands, brothers and fathers—but nonetheless, not caring for their relatives, they went to Kṛṣṇa. There was certainly fear, but this fear could not check their devotional service to Kṛṣṇa.
One should not mistakenly think that Lord Kṛṣṇa must be worshiped by an inimical attitude like that of Śiśupāla. The injunction is ānukūlyasya grahaṇaṁ prātikūlyasya varjanam: one should give up unfavorable activities and accept only favorable conditions in devotional service. Generally, if one blasphemes the Supreme Personality of Godhead he is punished. As the Lord says in Bhagavad-gītā (16.19).
(Srimad Bhagavatam----7:1:26----purport).