The spirit soul bewildered by the influence of false ego thinks himself the doer of activities that are in actuality carried out by the three modes of material nature.

Bg. 3.27

Three kinds of intelligence.

Understanding by which one knows what ought to be done and what ought not to be done, what is to be feared and what is not to be feared, what is binding and what is liberating, is in the mode of goodness.

Understanding which cannot distinguish between religion and irreligion, between action that should be done and action that should not be done, is in the mode of passion.

Understanding which considers irreligion to be religion and religion to be irreligion, under the spell of illusion and darkness, and strives always in the wrong direction, is in the mode of ignorance.

Bg. 18.30-32

Three kinds of knowledge.

According to the three different modes of material nature, there are three kinds of knowledge.

That knowledge by which one undivided spiritual nature is seen in all living entities, though they are divided into innumerable forms, you should understand to be in the mode of goodness.

That knowledge by which one sees that in every different body there is a different type of living entity you should understand to be in the mode of passion.

And that knowledge by which one is attached to one kind of work as the all in all, without knowledge of the truth, and which is very meager, is said to be in the mode of darkness.

Bg. 18.20-22

On austerity of the body, speech and mind.

Austerity of the body consists in worship of the Supreme Lord, the brāhmaṇas, the spiritual master, and superiors like the father and mother, and in cleanliness, simplicity, celibacy and nonviolence.

Austerity of speech consists in speaking words that are truthful, pleasing, beneficial, and not agitating to others, and also in regularly reciting Vedic literature.

And satisfaction, simplicity, gravity, self-control and purification of one’s existence are the austerities of the mind.

This threefold austerity, performed with transcendental faith by men not expecting material benefits but engaged only for the sake of the Supreme, is called austerity in goodness.

Bg. 17.14-17

Humility; pridelessness; nonviolence; tolerance; simplicity; approaching a bona fide spiritual master; cleanliness; steadiness; self-control; renunciation of the objects of sense gratification; absence of false ego; the perception of the evil of birth, death, old age and disease; detachment; freedom from entanglement with children, wife, home and the rest; even-mindedness amid pleasant and unpleasant events; constant and unalloyed devotion to Me; aspiring to live in a solitary place; detachment from the general mass of people; accepting the importance of self-realization; and philosophical search for the Absolute Truth – all these I declare to be knowledge, and besides this whatever there may be is ignorance.

Bg. 13.8-12

The Yaksha asked, “What constituteth the divinity of the Brahmanas? What even is their practice that is like that of the pious? What also is the human attribute of the Brahmanas? And what practice of theirs is like that of the impious?”
Yudhishthira answered, “The study of the Vedas constitutes their divinity: their asceticism constitutes behaviour that is like that of the pious; their liability to death is their human attribute and slander is their impiety.”
Mahabharata, Yaksha Prashna, 3