As stated in Bhagavad-gītā, the Supreme Personality of Godhead can be understood only by devotional service. Bhaktyā mām abhijānāti yāvān yaś cāsmi tattvataḥ (BG 18.55). If one wants to know the Supreme Personality of Godhead in truth, one must take to the activities of devotional service. These activities are called sattva or śuddha-sattva. In the material world, activities of goodness, which are symptomatic of a pure brāhmaṇa, are appreciated. But the activities of devotional service are śuddha-sattva; in other words, they are on the transcendental platform. Only by devotional service can one understand the Supreme.
Devotional service is called naiṣkarmya. Mere negation of material activity will not endure. Naiṣkarmyam apy acyuta-bhāva-varjitam. Unless one performs activities with reference to Kṛṣṇa consciousness, cessation of material activities will not be helpful. In hopes of achieving naiṣkarmya, freedom from material action, many highly elevated sannyāsīs stopped their activities, yet they failed and returned to the material platform to act as materialistic persons. But once one is engaged in the spiritual activities of bhakti-yoga, one does not fall down. Our Kṛṣṇa consciousness movement is therefore an attempt to engage everyone always in spiritual activity, by which one becomes transcendental to material actions. The spiritual activities of bhakti-mārga-śravaṇaṁ kīrtanaṁ viṣṇoḥ smaraṇaṁ pāda-sevanam (SB 7.5.23)—lead one to understand the Supreme Personality of Godhead. Therefore, as stated here, sattvena pratilabhyāya naiṣkarmyeṇa vipaścitā: "The Supreme Personality of Godhead is realized by pure devotees who act in the transcendental existence of bhakti-yoga."
The Gopāla-tāpanī Upaniṣad (15) says, bhaktir asya bhajanaṁ tad ihāmutropādhi-nairāsyenaivāmuṣmin manasaḥ kalpanam etad eva ca naiṣkarmyam. This is a definition of naiṣkarmya. One acts in naiṣkarmya when he fully engages in Kṛṣṇa conscious activities without material desires to enjoy, either here or in the upper planetary systems, in the present life or in a future life (iha-amutra). Anyābhilāṣitā-śūnyam [Bhakti-rasāmṛta-sindhu 1.1.11]. When one is freed from all contamination and he acts in devotional service under the direction of the spiritual master, one is on the platform of naiṣkarma. By such transcendental devotional service, the Lord is served. I offer my respectful obeisances unto Him.