In the prayers of Kuntī in the Śrīmad-Bhāgavatam (1.8.19) it is said that the Lord is covered by the curtain of yoga-māyā and thus ordinary people cannot understand Him. This yoga-māyā curtain is also confirmed in the Īśopaniṣad (mantra 15), in which the devotee prays:
hiraṇmayena pātreṇa
satyasyāpihitaṁ mukham
tat tvaṁ pūṣann apāvṛṇu
satya-dharmāya dṛṣṭaye
"O my Lord, You are the maintainer of the entire universe, and devotional service to You is the highest religious principle. Therefore, I pray that You will also maintain me. Your transcendental form is covered by the yoga-māyā. The brahmajyoti is the covering of the internal potency. May You kindly remove this glowing effulgence that impedes my seeing Your sac-cid-ānanda-vigraha [Bs. 5.1], Your eternal form of bliss and knowledge." The Supreme Personality of Godhead in His transcendental form of bliss and knowledge is covered by the internal potency of the brahmajyoti, and the less intelligent impersonalists cannot see the Supreme on this account.
(Bhavavad-Gita-7:25-purport).

This verse particularly mentions that even sages who are averse to the principles of devotional service to the Lord are also condemned to undergo the terms of material existence. Not only in this age, but formerly also, there were many sages who tried to invent their own systems of religion without reference to devotional service to the Supreme Lord, but there cannot be any religious principle without devotional service to the Lord. The Supreme Lord is the leader of the entire range of living entities, and no one can be equal to or greater than Him. Even the Lord's impersonal feature and all-pervading localized feature cannot be on an equal level with the Supreme Personality of Godhead. Therefore, there cannot be any religion or system of genuine philosophy for the advancement of the living entities without the principle of devotional service.
(Srimad Bhagavatam-3:9:10-purport).

“Anyone whose work is not meant for elevating him to religious life, anyone whose religious ritualistic performances do not raise him to renunciation, and anyone situated in renunciation that does not lead him to devotional service to the Supreme Personality of Godhead must be considered dead, although he is breathing.” The conclusion is that all pious activity, fruitive activity, religious principles and renunciation must ultimately lead to devotional service. There are different types of processes for rendering service. One may serve his country, people and society, the varṇāśrama-dharma system, the sick, the poor, the rich, women, demigods and so on. All this service comes under the heading of sense gratification, or enjoyment in the material world. It is most unfortunate that people are more or less attracted by such material activity and that the leaders of these activities are accepted as mahājanas, great ideal leaders. Actually they are only misleaders, but an ordinary man cannot understand how he is being misled.
(Sri Caitanya Caritamrta-2:17:185-purport).

The sages thus concluded that by following the principles of vaiṣṇava-dharma one becomes actually perfect, but that if one follows all the religious principles of a particular sect and does not become advanced in understanding the Supreme Personality of Godhead, Viṣṇu, all such labor of love is fruitless. To execute religious principles means to come to the platform of perfect knowledge. If one comes to the platform of perfect knowledge, then he will be uninterested in material affairs. Perfect knowledge means knowledge of one’s own self and the Supreme Self. The Supreme Self and the individual self, although one in quality, are different in quantity. This analytical understanding of knowledge is perfect. Simply to understand “I am not matter; I am spirit” is not perfect knowledge. The real religious principle is devotional service, or bhakti. This is confirmed in the Bhagavad-gītā, where Lord Kṛṣṇa says, “Give up all other religious principles and simply surrender unto Me.” Therefore, the term dharma applies only to vaiṣṇava-dharma, or bhagavad-dharma, by following which one automatically achieves all good qualities and advancements in life.
(Krsna Book-89).