CC Antya 9.68

sannyāsī virakta tomāra kā-sane sambandha?
vyavahāra lāgi’ tomā bhaje, sei jñāna-andha
Word for word: 
sannyāsī — a sannyāsī; virakta — one who has given up all connections with everyone; tomāra — Your; -sane — with whom; sambandha — relationship; vyavahāra lāgi’ — for some material purpose; tomā bhaje — worships You; sei — he; jñāna-andha — blind to all knowledge.
Translation: 
“You are a renounced sannyāsī. What connections do You have? One who worships You for some material purpose is blind to all knowledge.”
Purport: 

Becoming a devotee of the Lord to serve material purposes is a great mistake. Many people become showbottle devotees for material profits. Indeed, materialistic persons sometimes take to professional devotional service and keep Viṣṇu, the Supreme Personality of Godhead, as a means of livelihood. None of this, however, is approved. In the book known as Sapta-śatī, as mentioned by Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura, one can discover how a person worshiping the goddess Durgā begs her for different varieties of material profit. Such activities are very popular among people in general, but they are the attempts of foolish, blind people (sei jñāna-andha).

A materialist does not actually know why one should become a devotee. A devotee’s only concern is to satisfy the Supreme Personality of Godhead. Pure devotional service is defined by Śrīla Rūpa Gosvāmī:

anyābhilāṣitā-śūnyaṁjñāna-karmādy-anāvṛtam
ānukūlyena kṛṣṇānu-
śīlanaṁ bhaktir uttamā

One should be completely free from all material desires and should serve Kṛṣṇa simply to please Him. When people become interested in their own sense gratification (bhukti-mukti-siddhi-kāmī), some of them desire to enjoy the material world to the fullest extent, some of them desire to be liberated and merge into the existence of Brahman, and others want to perform magic through mystic power and thus become incarnations of God. These are all against the principles of devotional service. One must be free from all material desires. The desire of the impersonalist to merge into the existence of Brahman is also material because such an impersonalist wants to gratify his senses by merging into the existence of Kṛṣṇa instead of serving His lotus feet. Even if such a person merges into the Brahman effulgence, he falls down again into material existence. As stated in Śrīmad-Bhāgavatam (10.2.32):

āruhya kṛcchreṇa paraṁ padaṁ tataḥ
patanty adho ’nādṛta-yuṣmad-aṅghrayaḥ

Because Māyāvādī philosophers have no information regarding the transcendental service of the Lord, even after attaining liberation from material activities and merging into the Brahman effulgence, they must come down again to this material world.