One should not at any time tolerate blasphemy and insults against Lord Viṣṇu or His devotees. A devotee is generally very humble and meek, and he is reluctant to pick a quarrel with anyone. Nor does he envy anyone. However, a pure devotee immediately becomes fiery with anger when he sees that Lord Viṣṇu or His devotee is insulted. This is the duty of a devotee. Although a devotee maintains an attitude of meekness and gentleness, it is a great fault on his part if he remains silent when the Lord or His devotee is blasphemed.
(Srimad Bhagavatam-----4:14:32-----purport).

When human society individually or collectively becomes godless and blasphemes the authority of the Supreme Personality of Godhead, it is certainly destined for ruination. Such a civilization invites all kinds of bad fortune due to not appreciating the mercy of the Lord.
(Srimad Bhagavatam-----4:14:33-----purport).

The most grievous type of vaiṣṇava-aparādha is called gurv-aparādha, which refers to offenses at the lotus feet of the spiritual master. In the chanting of the holy name of the Supreme Personality of Godhead, this gurv-aparādha is considered the most grievous offense. Guror avajñā śruti-śāstra-nindanam (Padma Purāṇa). Among the ten offenses committed against the chanting of the holy name, the first offenses are disobedience of the spiritual master and blasphemy of the Vedic literature.
(Srimad Bhagavatam-----4:21:37-----purport).

"One who blasphemes a Vaiṣṇava cannot be protected by anyone. Even if a person is as strong as Lord Śiva, if he blasphemes a Vaiṣṇava, he is sure to be destroyed. This is the verdict of all śāstras. If one does not care for the verdict of the śāstras and dares blaspheme a Vaiṣṇava, he suffers life after life because of this."
(Srimad Bhagavatam-----5:10:25-----purport).

"Those who are envious and mischievous, who are the lowest among men, are cast by Me into the ocean of material existence, into various demoniac species of life. Attaining repeated birth amongst the species of demoniac life, such persons can never approach Me. Gradually they sink down to the most abominable type of existence." One who blasphemes the Lord is put into a family of asuras, in which there is every chance of forgetting the service of the Lord. Lord Kṛṣṇa further states in Bhagavad-gītā (9.11-12)
(Srimad Bhagavatam-----7:1:26-----purport).

A Vaiṣṇava is superior to a brāhmaṇa because whereas a brāhmaṇa knows that he is Brahman, not matter, a Vaiṣṇava knows that he is not only Brahman but also an eternal servant of the Supreme Brahman. Therefore, worship of a Vaiṣṇava is superior to worship of the Deity in the temple. Viśvanātha Cakravartī Ṭhākura says, sākṣād dharitvena samasta-śāstraiḥ: in all the scriptures the spiritual master, who is the best of the brāhmaṇas, the best of the Vaiṣṇavas, is considered to be as good as the Supreme Personality of Godhead. This does not mean, however, that the Vaiṣṇava thinks himself God, for this is blasphemous. Although a brāhmaṇa or Vaiṣṇava is worshiped as being as good as the Supreme Personality of Godhead, such a devotee always remains a faithful servant of the Lord and never tries to enjoy the prestige that might accrue to him from being the Supreme Lord's representative.
(Srimad Bhagavatam-----7:14:41-----purport).

As long as one is in the contamination of material existence, one changes bodies from the aquatics up to the position of Brahmā, but the human form of life is the highest perfectional life in the material world. The Vedas give directions by which to elevate oneself in the next life. The Vedas are the mother for such instructions, and the brāhmaṇas, or persons who are in knowledge of the Vedas, are the father. Thus if one blasphemes the Vedas and brāhmaṇas, naturally one goes down to the status of atheism. The exact word used in Sanskrit is nāstika, which refers to one who does not believe in the Vedas but manufactures some concocted system of religion.
(Srimad Bhagavatam-----4:2:30-----purport).

In the beginning of Śrīmad-Bhāgavatam it is established, tene brahma hṛdā: the Supreme Absolute Truth, the Personality of Godhead, instructed Brahmā in the Vedic knowledge through his heart. Therefore the evidence that Vedic knowledge is free from the defects of mistakes, illusions, cheating and imperfection is that it is spoken by the Supreme Personality of Godhead, Janārdana, and has thus been followed from time immemorial, beginning from Brahmā. The Vedic religion or the principles of the Vedas have been followed by the highly cultured population of India since time immemorial; no one can trace out the history of Vedic religion. Therefore it is sanātana, and any blasphemy against the Vedas is calculated to be atheism. The Vedas are described as setu, which means "a bridge." If one wants to attain his spiritual existence, one has to cross an ocean of nescience. The Vedas are the bridge by which to cross such a great ocean.
(Srimad Bhagavatam-----4:2:31-----purport).

The intelligence of cruel-minded persons is blinded by false pride based on great wealth, opulence, prestigious family connections, education, renunciation, personal beauty, physical strength and successful performance of Vedic rituals. Being intoxicated with this false pride, such cruel persons blaspheme the Supreme Personality of Godhead and His devotees.
(Srimad Bhagavatam-----11:5:9-----translation).

A candidate for spiritual advancement must be nonviolent, must follow in the footsteps of great ācāryas, must always remember the nectar of the pastimes of the Supreme Personality of Godhead, must follow the regulative principles without material desire and, while following the regulative principles, should not blaspheme others. A devotee should lead a very simple life and not be disturbed by the duality of opposing elements. He should learn to tolerate them.
(Srimad Bhagavatam-----4:22:24-----translation).

One should have firm faith that he will achieve all success in life by following those scriptures that describe the glories of the Supreme Personality of Godhead, Bhagavān. At the same time, one should avoid blaspheming other scriptures. One should rigidly control his mind, speech and bodily activities, always speak the truth, and bring the mind and senses under full control.
(Srimad Bhagavatam-----11:3:26-----translation).