In the phenomenal world three things are factually observed by any intelligent man: the living beings, the manifest world, and the ultimate control over them. The intelligent man can see that neither the living entity nor the phenomenal world are creations of chance. The symmetry of creation and its regulative actions and reactions suggests the plan of an intelligent brain behind them, and by genuine inquiry one may find out the ultimate cause with the help of one who knows them factually.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Srimad-Bhagavatam 2.5.2, Purport

The forgetful conditioned soul is educated by Krishna through the Vedic literatures, the realized spiritual master, and the Supersoul. Through these, he can understand the Supreme Personality of Godhead as He is, and he can understand that Lord Krishna is his eternal master and deliverer from the clutches of maya. In this way one can acquire real knowledge of his conditioned life and can come to understand how to attain liberation.
Sri Chaitanya Mahaprabhu
Sri Chaitanya-charitamrita, Madhyalila 20.123

A faithful man who is dedicated to transcendental knowledge and who subdues his senses is eligible to achieve such knowledge, and having achieved it he quickly attains the supreme spiritual peace. But ignorant and faithless persons who doubt the revealed scriptures do not attain God consciousness; they fall down. For the doubting soul there is happiness neither in this world nor in the next.
Lord Sri Krishna
Bhagavad-gita 4.39–40

My dear Lord, to understand those things beyond direct experience – such as spiritual liberation or the attainment of heaven and similar material enjoyments – and in general to understand the means and end of all things, it is imperative that the forefathers, demigods, and human beings consult the Vedic literatures, for these literatures, being Your own laws, constitute the highest evidence and revelation.
Sri Uddhava
Srimad-Bhagavatam 11.20.4

Pure love of God manifests as the most subtle consciousness, devoid of material qualities and material desires, increasing at every moment, and never interrupted.
Narada-bhakti-sutra 54

All you sons of immortality, hear, you who once resided in the divine kingdom!
Shvetashvatara Upanishad 2.5

By offering prayers in the company of the Maruts and other demigods, I always please the Supreme Personality of Godhead, Lord Govinda, whose form is eternal and full of knowledge and bliss, and who sits beneath a kalpa-vriksha tree.
Lord Brahma
Gopala-tapani Upanishad 1.38