The Supreme Lord Personality of Godhead is neither impersonal nor formless, but His body is nondifferent from Him, and therefore He is known as the embodiment of eternity, knowledge and bliss. In the Bṛhad-vaiṣṇava Tantra it is clearly mentioned that anyone who considers the form of Lord Kṛṣṇa to be made of material energy must be ostracized by all means. And if by chance the face of such an infidel is seen, one must clean himself by jumping in the river with his clothing.
(Srimad Bhagavatam-----1:15:35-----purport).

Especially for the householder devotees, the path of Deity worship is strongly recommended. As far as possible, every householder, by the direction of the spiritual master, must install the Deity of Viṣṇu, forms like Rādhā-Kṛṣṇa, Lakṣmī-Nārāyaṇa or Sītā-Rāma especially, or any other form of the Lord, like Nṛsiṁha, Varāha, Gaura-Nitāi, Matsya, Kūrma, śālagrāma-śilā and many other forms of Viṣṇu, like Trivikrama, Keśava, Acyuta, Vāsudeva, Nārāyaṇa and Dāmodara, as recommended in the Vaiṣṇava-tantras or Purāṇas, and one's family should worship strictly following the directions and regulations of arcana-vidhi.
(Srimad Bhagavatam-----2:3:35-----purport).

No one can introduce any new system into the Vedic way of life; if one does so out of malice, he is to be known as a pāṣaṇḍī, or atheist. In the Vaiṣṇava Tantra it is said:
yas tu nārāyaṇaṁ devaṁ
brahma-rudrādi-daivataiḥ
samatvenaiva vīkṣeta
sa pāṣaṇḍī bhaved dhruvam
(CC.2:18:116)
Although it is forbidden, there are many pāṣaṇḍīs who coin terms like daridra-nārāyaṇa and svāmi-nārāyaṇa, although not even such demigods as Brahmā and Śiva can be equal to Nārāyaṇa.
(Srimad Bhagavatam-----4:19:23-----purport).

Sometimes in revealed scriptures Lord Śiva is described as being nondifferent from the Supreme Personality of Godhead. The point is that Lord Śiva and Lord Viṣṇu are so intimately connected that there is no difference in opinion. The actual fact is, ekale īśvara kṛṣṇa, āra saba bhṛtya: "The only supreme master is Kṛṣṇa, and all others are His devotees or servants." (CC.1:5:142) This is the real fact, and there is no difference of opinion between Lord Śiva and Lord Viṣṇu in this connection. Nowhere in revealed scripture does Lord Śiva claim to be equal to Lord Viṣṇu. This is simply the creation of the so-called devotees of Lord Śiva, who claim that Lord Śiva and Lord Viṣṇu are one. This is strictly forbidden in the Vaiṣṇava-tantra: yas tu nārāyaṇaṁ devam (CC.2:18:116). Lord Viṣṇu, Lord Śiva and Lord Brahmā are intimately connected as master and servants. Śiva-viriñci-nutam (S.B.11:5:33). Viṣṇu is honored and offered obeisances by Lord Śiva and Lord Brahmā. To consider that they are all equal is a great offense. They are all equal in the sense that Lord Viṣṇu is the Supreme Personality of Godhead and all others are His eternal servants.
(Srimad Bhagavatam-----4:30:38-----purport).

There are many Vaiṣṇava families in Bengal whose members, although not actually born brāhmaṇas, act as ācāryas by initiating disciples and offering the sacred thread as enjoined in the Vaiṣṇava tantras. For example, in the families of Ṭhākura Raghunandana Ācārya, Ṭhākura Kṛṣṇadāsa, Navanī Hoḍa and Rasikānanda-deva (a disciple of Śyāmānanda Prabhu), the sacred thread ceremony is performed, as it is for the caste Gosvāmīs, and this system has continued for the past three to four hundred years. Accepting disciples born in brāhmaṇa families, they are bona fide spiritual masters who have the facility to worship the śālagrāma-śilā, which is worshiped with the Deity. As of this writing, śālagrāma-śilā worship has not yet been introduced in our Kṛṣṇa consciousness movement, but soon it will be introduced in all our temples as an essential function of arcana-mārga (Deity worship).
(Sri Caitanya Caritamrta-----1:7:45-----purport).

It is offensive to think that Balarāma is superior to Lord Rāmacandra or vice versa. Neophyte devotees do not understand this śāstric conclusion, and consequently they unnecessarily create an offensive situation. In text 154 Śrī Caitanya Mahāprabhu clarified this in a very lucid way: īśvaratve bheda mānile haya aparādha. "It is offensive for one to differentiate between the forms of the Lord." On the other hand, one should not think that the forms of the Lord are the same as the forms of the demigods. This is certainly offensive, as confirmed by the Vaiṣṇava-tantra:
yas tu nārāyaṇaṁ devaṁ brahma-rudrādi-daivataiḥ
samatvenaiva vīkṣeta sa pāṣaṇḍī bhaved dhruvam
(CC.2:18:116)
"A pāṣaṇḍī is one who considers the great demigods such as Lord Brahmā and Lord Śiva equal to the Supreme Personality of Godhead, Nārāyaṇa." (Hari-bhakti-vilāsa 7.117)
The conclusion is that we should neither differentiate between the forms of the Lord nor equate the forms of the Lord with the forms of demigods or human beings.
(Sri Caitanya Caritamrta-----2:9;155-----purport).

When Lord Caitanya thus heard Himself equated with Kṛṣṇa, He mildly protested. He wanted to warn people in general not to compare the Supreme Lord with any living entity, and although He was the Supreme Lord Himself, He protested against this comparison in order to teach us. Thus He said that it is the greatest offense to compare anyone with the Supreme Lord Kṛṣṇa. Lord Caitanya always maintained that Viṣṇu, the Supreme Personality of Godhead, is great and the living entities, however great they may be, are but infinitesimal. In this connection, He quoted a verse from Padma Purāṇa which is found in the Vaiṣṇava tantra (Hari-bhakti-vilāsa 1.73): "A person who compares the Supreme Lord even with the greatest of demigods like Brahmā and Śiva must be considered a number one atheist."
(Teachings of Lord Caitanya).

Even thinking of the demigods cannot compare with thinking of Kṛṣṇa. It is warned in the vaiṣṇava-tantra that one who puts Viṣṇu, Nārāyaṇa or Kṛṣṇa on the same level as the demigods is called a pāṣaṇḍī, or rascal. On hearing this question from Mahārāja Parīkṣit, Śukadeva Gosvāmī replied, "My dear King, your question is already answered, even before this incident." Because Parīkṣit Mahārāja wanted to clear up the situation, his spiritual master answered him very intelligently, "Why are you again asking about the same subject matter which has already been explained to you? Why are you so forgetful?" A spiritual master is always in the superior position, so he has the right to chastise his disciple in this way. Śukadeva Gosvāmī knew that Mahārāja Parīkṣit asked the question not for his own understanding but as a warning to the future innocent people who might think others to be equal to Kṛṣṇa.
(Krsna Book).