The desire to merge into the impersonal Brahman is the subtlest type of atheism. As soon as such atheism, disguised in the dress of liberation, is encouraged, one becomes completely unable to traverse the path of devotional service to the Supreme Personality of Godhead.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Sri Chaitanya-charitamrita, Adi 1.92, Purport

If we want to follow the path of true auspiciousness, we should give up the countless opinions of people and only hear the words of the Vedas.
Srila Bhaktisiddhanta Sarasvati Thakura
64 Principles for Community, Principle 13

Desire, anger, greed, bewilderment, intoxication, and pride are six enemies that wait on the path of a soul’s journey of life. They have lassoes which pull that soul so he slips from righteousness and performs unscrupulous activities. These enemies pull tightly to drag away one’s life.
Srila Bhaktivinoda Thakura
Manah-shiksha Bhasha, Song Five

When one understands that the Supreme Personality of Godhead and the individual spirit souls are eternally distinct entities, then he may become qualified for liberation and for living eternally in the spiritual world.
Svetashvatara Upanishad 1.6

Simply by material birth, human beings become attached within their minds to personal sense gratification, long duration of life, sense activities, bodily strength, sexual potency, and friends and family. Their minds are thus absorbed in that which defeats their actual self-interest.
Lord Sri Krishna
Srimad-Bhagavatam 11.21.24

Therefore, my dear King, the living entity, who has a subtle mental covering, develops all kinds of thoughts and images because of his previous body. Take this from me as certain. There is no possibility of concocting anything mentally without having perceived it in the previous body.
Sri Narada Muni
Srimad-Bhagavatam 4.29.65

Caught in the grip of ignorance, self-proclaimed experts consider themselves learned authorities. They wander about this world befooled, like the blind leading the blind.
Katha Upanishad 1.2.5

The essence of all Vedic knowledge – comprehending the three kinds of Vedic activity [karma-kanda, jnana-kanda, and upasana-kanda], the chandas, or Vedic hymns, and the processes for satisfying the demigods – is included in the eight syllables Hare Krishna, Hare Krishna. This is the reality of all Vedanta. The chanting of the holy name is the only means to cross the ocean of nescience.
Narada Pancharatra
Quoted in Sri Chaitanya-charitamrita, Adi 7.76, Purport

Dearer to the Lord than even His own beautiful form, His easily worshiped holy name benefits the entire world. Indeed, nothing is as full of nectar as the holy name of the Lord.
The Vaikuntha-dutas
Sri Brihad-bhagavatamrita 2.3.184

A wise man who understands the Supreme falls in love with Him.
Brihad-aranyaka Upanishad 4.4.21