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.
Out of many standard and authoritative revealed scriptures, the Bhagavad-gītā is the best. Persons who are almost like animals have no faith in, or knowledge of, the standard revealed scriptures; and some, even though they have knowledge of, or can cite passages from, the revealed scriptures, have actually no faith in these words. And even though others may have faith in scriptures like Bhagavad-gītā, they do not believe in or worship the Personality of Godhead, Śrī Kṛṣṇa. Such persons cannot have any standing in Kṛṣṇa consciousness. They fall down. Out of all the above-mentioned persons, those who have no faith and are always doubtful make no progress at all. Men without faith in God and His revealed word find no good in this world, nor in the next. For them there is no happiness whatsoever. One should therefore follow the principles of revealed scriptures with faith and thereby be raised to the platform of knowledge. Only this knowledge will help one become promoted to the transcendental platform of spiritual understanding. In other words, doubtful persons have no status whatsoever in spiritual emancipation. One should therefore follow in the footsteps of great ācāryas who are in the disciplic succession and thereby attain success.
(Bhagavad-Gita-----4:40-----translation and purport).

One who acts in devotional service, renouncing the fruits of his actions, and whose doubts have been destroyed by transcendental knowledge, is situated factually in the self. Thus he is not bound by the reactions of work, O conqueror of riches.
One who follows the instruction of the Bhagavad-gītā, as it is imparted by the Lord, the Personality of Godhead Himself, becomes free from all doubts by the grace of transcendental knowledge. He, as a part and parcel of the Lord, in full Kṛṣṇa consciousness, is already established in self-knowledge. As such, he is undoubtedly above bondage to action.
(Bhagavad-Gita-----4:41-----translation and purport).

Therefore the doubts which have arisen in your heart out of ignorance should be slashed by the weapon of knowledge. Armed with yoga, O Bhārata, stand and fight.
(Bhagavad-Gita-----4:42-----translation).

Kṛṣṇa consciousness is awakened by different types of sacrifices to the demigods, sacrifice to Brahman, sacrifice in celibacy, in household life, in controlling the senses, in practicing mystic yoga, in penance, in forgoing material possessions, in studying the Vedas, and in partaking of the social institution called varṇāśrama-dharma. All of these are known as sacrifice, and all of them are based on regulated action. But within all these activities, the important factor is self-realization. One who seeks that objective is the real student of Bhagavad-gītā, but one who doubts the authority of Kṛṣṇa falls back. One is therefore advised to study Bhagavad-gītā, or any other scripture, under a bona fide spiritual master, with service and surrender. A bona fide spiritual master is in the disciplic succession from time eternal, and he does not deviate at all from the instructions of the Supreme Lord as they were imparted millions of years ago to the sun-god, from whom the instructions of Bhagavad-gītā have come down to the earthly kingdom. One should, therefore, follow the path of Bhagavad-gītā as it is expressed in the Gītā itself and beware of self-interested people after personal aggrandizement who deviate others from the actual path. The Lord is definitely the supreme person, and His activities are transcendental. One who understands this is a liberated person from the very beginning of his study of Bhagavad-gītā.
(Bhagavad-Gita-----4:42------purport).

Those who are beyond the dualities that arise from doubts, whose minds are engaged within, who are always busy working for the welfare of all living beings, and who are free from all sins achieve liberation in the Supreme.
(Bhagavad-Gita-----5:25-----translation).

This is my doubt, O Kṛṣṇa, and I ask You to dispel it completely. But for You, no one is to be found who can destroy this doubt.
Kṛṣṇa is the perfect knower of past, present and future. In the beginning of the Bhagavad-gītā, the Lord said that all living entities existed individually in the past, they exist now in the present, and they continue to retain individual identity in the future, even after liberation from the material entanglement. So He has already cleared up the question of the future of the individual living entity. Now, Arjuna wants to know of the future of the unsuccessful transcendentalist. No one is equal to or above Kṛṣṇa, and certainly the so-called great sages and philosophers who are at the mercy of material nature cannot equal Him. Therefore the verdict of Kṛṣṇa is the final and complete answer to all doubts, because He knows past, present and future perfectly—but no one knows Him. Kṛṣṇa and Kṛṣṇa conscious devotees alone can know what is what.
(Bhagavad-Gita-----6:39-----translation and purport).

The Supreme Personality of Godhead said: Now hear, O son of Pṛthā, how by practicing yoga in full consciousness of Me, with mind attached to Me, you can know Me in full, free from doubt.
In this Seventh Chapter of Bhagavad-gītā, the nature of Kṛṣṇa consciousness is fully described. Kṛṣṇa is full in all opulences, and how He manifests such opulences is described herein. Also, four kinds of fortunate people who become attached to Kṛṣṇa and four kinds of unfortunate people who never take to Kṛṣṇa are described in this chapter.
In the first six chapters of Bhagavad-gītā, the living entity has been described as nonmaterial spirit soul capable of elevating himself to self-realization by different types of yogas. At the end of the Sixth Chapter, it has been clearly stated that the steady concentration of the mind upon Kṛṣṇa, or in other words Kṛṣṇa consciousness, is the highest form of all yoga. By concentrating one's mind upon Kṛṣṇa, one is able to know the Absolute Truth completely, but not otherwise. Impersonal brahma-jyotir or localized Paramātmā realization is not perfect knowledge of the Absolute Truth, because it is partial. Full and scientific knowledge is Kṛṣṇa, and everything is revealed to the person in Kṛṣṇa consciousness. In complete Kṛṣṇa consciousness one knows that Kṛṣṇa is ultimate knowledge beyond any doubts. Different types of yoga are only steppingstones on the path of Kṛṣṇa consciousness. One who takes directly to Kṛṣṇa consciousness automatically knows about brahma-jyotir and Paramātmā in full. By practice of Kṛṣṇa consciousness yoga, one can know everything in full—namely the Absolute Truth, the living entities, the material nature, and their manifestations with paraphernalia.
(Bhagavad-Gita-----7:1-----translation and purport).

Arjuna addresses the Lord as Madhusūdana because Kṛṣṇa once killed a demon named Madhu. Actually these questions, which are of the nature of doubts, should not have arisen in the mind of Arjuna, because Arjuna is a Kṛṣṇa conscious devotee. Therefore these doubts are like demons. Since Kṛṣṇa is so expert in killing demons, Arjuna here addresses Him as Madhusūdana so that Kṛṣṇa might kill the demonic doubts that arise in Arjuna's mind.
(Bhagavad-Gita-----8:2-----purport).

Intelligence, knowledge, freedom from doubt and delusion, forgiveness, truthfulness, control of the senses, control of the mind, happiness and distress, birth, death, fear, fearlessness, nonviolence, equanimity, satisfaction, austerity, charity, fame and infamy—all these various qualities of living beings are created by Me alone.
(Bhagavad-Gita-----10:4-5-----translation).

Asammoha, freedom from doubt and delusion, can be achieved when one is not hesitant and when he understands the transcendental philosophy. Slowly but surely he becomes free from bewilderment. Nothing should be accepted blindly; everything should be accepted with care and with caution. Kṣamā, tolerance and forgiveness, should be practiced; one should be tolerant and excuse the minor offenses of others. Satyam, truthfulness, means that facts should be presented as they are, for the benefit of others. Facts should not be misrepresented. According to social conventions, it is said that one can speak the truth only when it is palatable to others. But that is not truthfulness. The truth should be spoken in a straightforward way, so that others will understand actually what the facts are. If a man is a thief and if people are warned that he is a thief, that is truth. Although sometimes the truth is unpalatable, one should not refrain from speaking it. Truthfulness demands that the facts be presented as they are for the benefit of others. That is the definition of truth.
(Bhagavad-Gita-----10:4-5-----purport).