In the scriptures it is instructed that one may worship a certain demigod if he is desirous of achieving some material gain. For example, one is advised to worship the sun god if he is desirous of getting rid of a diseased condition. For a beautiful wife, one can worship Umā, the wife of Lord Śiva, and for advanced education one may worship Sarasvatī. Similarly, there is a list in the Śrīmad-Bhāgavatam for worshipers of all demigods, according to different material desires. But all of these worshipers, although they appear to be very good devotees of the demigods, are still considered to be nondevotees. They cannot be accepted as devotees.
The māyāvādīs (impersonalists) say that one can worship any form of the Lord and that it doesn't matter because one reaches the same destination anyway. But it is clearly stated in the Bhagavad-gītā that those who are worshipers of the demigods will ultimately reach only the planets of those demigods, while those who are devotees of the Lord Himself will be promoted to the Lord's abode, the kingdom of God. So actually these persons who are worshipers of demigods have been condemned in the Gītā.
It is described that due to their lusty desires they have lost their intelligence, and therefore they have taken to worshiping the different demigods. So in the Viṣṇu-rahasya these demigod worshipers are forcefully condemned by the statement that it is better to live with the most dangerous animals than to associate with these persons.
Another stricture is that a person may have many disciples, but he should not act in such a way that he will be obliged to any of them for some particular action or some favor. And one should also not be very enthusiastic about constructing new temples, nor should one be enthusiastic about reading various types of books, save and except the ones which lead to the advancement of devotional service. Practically, if one very carefully reads the Bhagavad-gītā, Śrīmad-Bhāgavatam, Teachings of Lord Caitanya and this Nectar of Devotion, that will give him sufficient knowledge to understand the science of Kṛṣṇa consciousness. One need not take the trouble of reading other books.
In the Seventh Canto of Śrīmad-Bhāgavatam, 13th Chapter, 7th verse, Nārada Muni, while discussing with Mahārāj Yudhiṣṭhira the various functions of the different orders in society, especially mentions rules for the sannyāsīs—those persons who have renounced this material world. One who has accepted the sannyāsa order of life is forbidden to accept as a disciple anyone who is not fit. A sannyāsī should first of all examine whether a prospective student is sincerely seeking Kṛṣṇa consciousness. If he is not, he should not be accepted. However, Lord Caitanya's causeless mercy is such that He advised all bona fide spiritual masters to speak about Kṛṣṇa consciousness everywhere. Therefore, in the line of Lord Caitanya, even the sannyāsīs can speak about Kṛṣṇa consciousness everywhere, and if someone is seriously inclined to become a disciple, the sannyāsī always accepts him.