The activities of the living entity in the body of a dog may be experienced in the mind of a different body; therefore those activities appear never to have been heard or seen. The mind continues, although the body changes. Even in this life-span we can sometimes experience dreams of our childhood. Although such incidents now appear strange, it is to be understood that they are recorded in the mind. Because of this, they become visible in dreams. The transmigration of the soul is caused by the subtle body, which is the storehouse of all kinds of material desires. Unless one is fully absorbed in Kṛṣṇa consciousness, material desires will come and go.
(Srimad Bhagavatam----4:29:68----purport).

Why we see things not experienced in this life is explained herein. That which we see is the future expression of a gross body or is already stocked in our mental stockpile. Because a Kṛṣṇa conscious person does not have to accept a future gross body, his recorded desires are fulfilled in a dream. We therefore sometimes find things in a dreamnever experienced in our present life.
(Srimad Bhagavatam----4:29:69----purport).

When a living entity is within the womb, his gross body, the ten sense organs and the mind are not fully developed. At such a time the objects of the senses do not disturb him. In a dream a young man may experience the presence of a young woman because at that time the senses are active. Because of undeveloped senses, a child or boy will not see a young woman in his dreams. The senses are active in youth even when one dreams, and although there may be no young woman present, the senses may act and there may be a seminal discharge (nocturnal emission). The activities of the subtle and gross bodies depend on how developed conditions are.
(Srimad Bhagavatam----4:29:72----purport).

When the living entity dreams, the sense objects are not actually present. However, because one has associated with the sense objects, they become manifest. Similarly, the living entity with undeveloped senses does not cease to exist materially, even though he may not be exactly in contact with the sense objects.
(Srimad Bhagavatam----4:29:73----purport).

This material creation is the spirit soul's dream. Actually all existence in the material world is a dream of Mahā-viṣṇu, as the Brahma-saṁhitā describes:
yaḥ kāraṇārṇava-jale bhajati sma yoga-
nidrām ananta-jagad-aṇḍa-saroma-kūpaḥ
(Bs. 5.47)
This material world is created by the dreaming of Mahā-viṣṇu. The real, factual platform is the spiritual world, but when the spirit soul wants to imitate the Supreme Personality of Godhead, he is put into this dreamland of material creation. After being in contact with the material modes of nature, the living entity develops the subtle and gross bodies. When the living entity is fortunate enough to associate with Śrī Nārada Mahāmuni or his servants, he is liberated from this dreamland of material creation and the bodily conception of life.
(Srimad Bhagavatam----4:29:83----purport).

"After attaining Me, the great souls, who are yogīs in devotion, never return to this temporary world, which is full of miseries, because they have attained the highest perfection." And what is that highest perfection? That is also explained in that verse. The highest perfection is to return home, back to Godhead, so that one will not have to return to this material world and transmigrate from one body to another in the dream of material existence. By the grace of Lord Śiva, the Pracetās actually attained perfection and returned home, back to Godhead, after enjoying material facilities to the highest extent. Maitreya will now narrate that to Vidura.
(Srimad Bhagavatam----4:30:1----purport).

Even if one is liberated, he nevertheless accepts the body he has received according to his past karma. Without misconceptions, however, he regards his enjoyment and suffering due to that karma the way an awakened person regards a dream he had while sleeping. He thus remains steadfast and never works to achieve another material body under the influence of the three modes of material nature.
The difference between a liberated and conditioned soul is that the conditioned soul is under the concept of bodily life, whereas a liberated person knows that he is not the body but a spirit, different from the body. Priyavrata might have thought that although a conditioned soul is forced to act according to the laws of nature, why should he, who was far advanced in spiritual understanding, accept the same kind of bondage and impediments to spiritual advancement? To answer this doubt, Lord Brahmā informed him that even those who are liberated do not resent accepting, in the present body, the results of their past activities. While sleeping, one dreams many unreal things, but when he awakens he disregards them and makes progress in factual life.
(Srimad Bhagavatam----5:1:16----translation and purport).

This is a discussion on impersonal Māyāvāda philosophy and the practical philosophy of Vaiṣṇavas. The Māyāvāda philosophy explains this phenomenal world to be false, but Vaiṣṇava philosophers do not agree. They know that the phenomenal world is a temporary manifestation, but it is not false. A dream that we see at night is certainly false, but a horrible dream certainly affects the person seeing it. The soul's fatigue is not factual, but as long as one is immersed in the illusory bodily conception, one is affected by such false dreams. When dreaming, it is not possible to avoid the actual facts, and the conditioned soul is forced to suffer due to his dream. A waterpot is made of earth and is temporary. Actually there is no waterpot; there is simply earth. However, as long as the waterpot can contain water, we can use it in that way. It cannot be said to be absolutely false.
(Srimad Bhagavatam----5:10:21----purport).

A dream becomes automatically known to a person as false and immaterial, and similarly one eventually realizes that material happiness in this life or the next, on this planet or a higher planet, is insignificant. When one realizes this, the Vedas, although an excellent source, are insufficient to bring about direct knowledge of the truth.
In Bhagavad-gītā (2.45), Kṛṣṇa advised Arjuna to become transcendental to the material activities impelled by the three material modes of nature (traiguṇya-viṣayā vedā nistraiguṇyo bhavārjuna). The purpose of Vedic study is to transcend the activities of the three modes of material nature. Of course in the material world the mode of goodness is accepted as the best, and one can be promoted to the higher planetary systems by being on the sattva-guṇa platform. However, that is not perfection. One must come to the conclusion that even the sattva-guṇa platform is also not good. One may dream that he has become a king with a good family, wife and children, but immediately at the end of that dream he comes to the conclusion that it is false.
(Srimad Bhagavatam----5:11:3----translation and purport).

By bhakti-yoga one can completely avoid the tendency for sinful life; other methods are not very feasible. Therefore the Vedic literature concludes that devotional service is more important than the methods of karma-kāṇḍa and jñāna-kāṇḍa. Only the path of devotional service is auspicious for everyone. Fruitive activities and speculative knowledge cannot independently liberate anyone, but devotional service, independent of karma and jñāna, is so potent that one who has fixed his mind at the lotus feet of Kṛṣṇa is guaranteed not to meet the Yamadūtas, the order carriers of Yamarāja, even in dreams.
(Srimad Bhagavatam----6:1---summary).

Parīkṣit Mahārāja had inquired from Śukadeva Gosvāmī how one can be saved from falling into the various conditions of hellish life. In this verse Śukadeva Gosvāmī answers that a soul who has surrendered to Kṛṣṇa certainly cannot go to naraka, hellish existence. To say nothing of going there, even in his dreams he does not see Yamarāja or his order carriers, who are able to take one there. In other words, if one wants to save himself from falling into naraka, hellish life, he should fully surrender to Kṛṣṇa. The word sakṛt is significant because it indicates that if one sincerely surrenders to Kṛṣṇa once, he is saved even if by chance he falls down by committing sinful activities.
(Srimad Bhagavatam----6:1:19----purport).

There are two stages of God realization. One is called sujñeyam, or very easily understood (generally by mental speculation), and the other is called durjñeyam, understood only with difficulty. Paramātmā realization and Brahman realization are considered sujñeyam, but realization of the Supreme Personality of Godhead is durjñeyam. As described here, one attains the ultimate realization of the Personality of Godhead when one gives up the activities of the mind—thinking, feeling and willing—or, in other words, when mental speculation stops. This transcendental realization is above suṣupti, deep sleep. In our gross conditional stage we perceive things through material experience and remembrance, and in the subtle stage we perceive the world in dreams. The process of vision also involves remembrance and also exists in a subtle form. Above gross experience and dreams is suṣupti, deep sleep, and when one comes to the completely spiritual platform, transcending deep sleep, he attains trance, viśuddha-sattva, or vasudeva-sattva, in which the Personality of Godhead is revealed.
(Srimad Bhagavatam----6:4:26----purport).

The Māyāvādī philosophers say, brahma satyaṁ jagan mithyā: Brahman, the living being, is factual, but his present bodily situation is false. According to the Vaiṣṇava philosophy, however, the present situation is not false but temporary. It is like a dream. A dream does not exist before one falls asleep, nor does it continue after one awakens. The period for dreaming exists only between these two, and therefore it is false in the sense that it is impermanent. Similarly, the entire material creation, including our own creation and those of others, is impermanent. We do not lament for the situation in a dream before the dream takes place or after it is over, and so during the dream, or during a dreamlike situation, one should not accept it as factual and lament about it. This is real knowledge.
(Srimad Bhagavatam----6:15:5----purport).

These visible objects like wife, children and property are like dreams and mental concoctions. Actually what we see has no permanent existence. It is sometimes seen and sometimes not. Only because of our past actions do we create such mental concoctions, and because of these concoctions, we perform further activities.
Everything material is a mental concoction because it is sometimes visible and sometimes not. At night when we dream of tigers and snakes, they are not actually present, but we are afraid because we are affected by what we envision in our dreams. Everything material is like a dream because it actually has no permanent existence.
Śrīla Viśvanātha Cakravartī Ṭhākura writes as follows in his commentary: arthena vyāghra-sarpādinā vinaiva dṛśyamānāḥ svapnādi-bhaṅge sati na dṛśyante tad evaṁ dārādayo 'vāstava-vastu-bhūtāḥ svapnādayo 'vastu-bhūtāś ca sarve manobhavāḥ mano-vāsanā janyatvān manobhavāḥ. At night one dreams of tigers and snakes, and while dreaming he actually sees them, but as soon as the dream is broken they no longer exist.
(Srimad Bhagavatam----6:15:24----translation and purport).

For example, the brain is nothing but matter, but when electrified by the energy of the Supreme Personality of Godhead, the brain can act, just as iron can burn when made red-hot by the influence of fire. The brain can act while we are awake or even while we are dreaming, but when we are fast asleep or unconscious the brain is inactive. Since the brain is a lump of matter, it does not have independent power with which to act. It can act only when favored by the influence of the Supreme Personality of Godhead, who is Brahman or Para-brahman. This is the way to understand how the Supreme Brahman, Kṛṣṇa, is present everywhere, just as the sunshine is present because of the sun-god in the sun globe. The Supreme Lord is called Hṛṣīkeśa; He is the only conductor of the senses. Unless empowered by His energy, our senses cannot act. In other words, He is the only seer, the only worker, the only listener, and the only active principle or supreme controller.
(Srimad Bhagavatam----6:16:24----purport).

The categories of emanations from the nonsubstance are two—activities and forbidden activities (karma and vikarma). Karma refers to the pious life or material activities performed during the day and the mental activities of dreams at night. These are more or less desired activities. Vikarma, however, refers to illusory activities, which are something like the will-o'-the-wisp. These are activities that have no meaning. For example, modern scientists imagine that life can be produced from chemical combinations, and they are very busy trying to prove this in laboratories throughout the world, although no one in history has been able to produce the substance of life from material combinations. Such activities are called vikarma.
(Srimad Bhagavatam----6:16:51----purport).