In Bhagavad-gītā (9.25) it is said, pitṟn yānti pitṛ-vratāḥ. Those who are interested in family welfare are called pitṛ-vratāḥ. There is a planet called Pitṛloka, and the predominating deity of that planet is called Aryamā. He is somewhat of a demigod, and by satisfying him one can help ghostly family members develop a gross body. Those who are very sinful and attached to their family, house, village or country do not receive a gross body made of material elements but remain in a subtle body, composed of mind, ego and intelligence. Those who live in such subtle bodies are called ghosts. This ghostly position is very painful because a ghost has intelligence, mind and ego and wants to enjoy material life, but because he doesn't have a gross material body, he can only create disturbances for want of material satisfaction. It is the duty of family members, especially the son, to offer oblations to the demigod Aryamā or to Lord Viṣṇu. From time immemorial in India the son of a dead man goes to Gayā and, at a Viṣṇu temple there, offers oblations for the benefit of his ghostly father. It is not that everyone's father becomes a ghost, but the oblations of piṇḍa are offered to the lotus feet of Lord Viṣṇu so that if a family member happens to become a ghost, he will be favored with a gross body.
(Srimad Bhagavatam----4:18:18----purport).

It is important to know thoroughly the process of creation as it applies to this cosmic manifestation. Similarly, this body is also created according to the same process by the Supreme Lord. The Personality of Godhead, after entering the universe, creates the cosmic manifestations one after another. Similarly, the living entity, after entering a womb of a mother, also collects his gross and subtle bodies, taking ingredients from the totality of sky, air, fire, water and earth. The words yathā-sthānaṁ vibhāgaśaḥ indicate that one should know the process of creation and should meditate upon the creative process inversely and thus become free from material contamination.
(Srimad Bhagavatam----4:23:16----purport).

The living entity is covered by two different types of bodies—the gross body and the subtle body. At death we can see that the gross body is finished, but actually the living entity is carried by the subtle body to another gross body. The so-called scientists of the modern age cannot see how the subtle body is working in carrying the soul from one body to another. This subtle body has been figuratively described as a serpent, or the city's police superintendent. When there is fire everywhere, the police superintendent cannot escape either. When there is security and an absence of fire in the city, the police superintendent can impose his authority upon the citizens, but when there is an all-out attack on the city, he is rendered useless. As the life air was ready to leave the gross body, the subtle body also began to experience pain.
(Srimad Bhagavatam----4:28:13----purport).

It is clear in this verse that at the time of death thoughts of material enjoyment do not go away. This indicates that the living entity, the soul, is carried by the subtle body—mind, intelligence and ego. Due to false ego, the living entity still wants to enjoy the material world, and for want of material enjoyment he becomes sorry or sad. He still makes intellectual plans to further his existence, and therefore, although he gives up the gross body, he is carried by the subtle body to another gross body. The transmigration of the subtle bodyis never visible to material eyes; therefore when one gives up the gross body, we think that he is finished. Plans for material enjoyment are made by the subtle body, and the gross body is the instrument for enjoying these plans. Thus the gross body can be compared to the wife, for the wife is the agent for all kinds of sense gratification. Because of long association with the gross body, the living entity becomes very sad to be separated from it. The mental activity of the living entity obliges him to accept another gross body and continue his material existence.
(Srimad Bhagavatam----4:28:17----purport).

Because of his desire to enjoy the material world, the living entity is dressed with the material gross and subtle bodies. Thus he is given a chance to enjoy the senses. The senses are therefore the instruments for enjoying the material world; consequently the senses have been described as friends. Sometimes, because of too much sinful activity, the living entity does not get a material gross body, but hovers on the subtle platform. This is called ghostly life. Because of his not possessing a gross body, he creates a great deal of trouble in his subtle body. Thus the presence of a ghost is horrible for those who are living in the gross body. As stated in Bhagavad-gītā (15.10):
utkrāmantaṁ sthitaṁ vāpi
bhuñjānaṁ vā guṇānvitam
vimūḍhā nānupaśyanti
paśyanti jñāna-cakṣuṣaḥ
"The foolish cannot understand how a living entity can quit his body, nor can they understand what sort of body he enjoys under the spell of the modes of nature. But one whose eyes are trained in knowledge can see all this."
(Srimad Bhagavatam----4:29:6----purport).

Atheists want evidence for the resultant actions of past activities. Therefore they ask, "Where is the proof that I am suffering and enjoying the resultant actions of past karma?" They have no idea how the subtle body carries the results of the present body's actions down to the next gross body. The present body may be finished grossly, but the subtle body is not finished; it carries the soul to the next body. Actually the gross body is dependent on the subtle body. Therefore the next gross body must suffer and enjoy according to thesubtle body. The soul is carried by the subtle body continuously until liberated from gross material bondage.
(Srimad Bhagavatam----4:29:59----purport).

The living entity has two kinds of body—the subtle body and the gross body. Actually he enjoys through the subtle body, which is composed of mind, intelligence and ego. The gross body is the instrumental outer covering. When the gross body is lost, or when it dies, the root of the gross body—the mind, intelligence and ego—continues and brings about another gross body. Although the gross bodies apparently change, the real root of the gross body—the subtle body of mind, intelligence and ego—is always there. The subtle body's activities—be they pious or impious—create another situation for the living entity to enjoy or suffer in the next gross body. Thus the subtle body continues whereas the gross bodies change one after another.
(Srimad Bhagavatam----4:29:60----purport).

Since modern scientists and philosophers are too materialistic, and since their knowledge is taken away by the illusory energy, they cannot explain how the gross body is changing. The materialistic philosopher Darwin has tried to study the changes of the gross body, but because he had no knowledge of either the subtle body or the soul, he could not clearly explain how the evolutionary process is going on. One may change the gross body, but he works in the subtle body. People cannot understand the activities of the subtle body, and consequently they are bewildered as to how the actions of one gross body affect another gross body. The activities of the subtle body are also guided by the Supersoul, as explained in Bhagavad-gītā (15.15):
sarvasya cāhaṁ hṛdi sanniviṣṭo
mattaḥ smṛtir jñānam apohanaṁ ca
"I am seated in everyone's heart, and from Me come remembrance, knowledge and forgetfulness."
(Srimad Bhagavatam----4:29:60----purport).

Although the root of distress and happiness is the mind, intelligence and ego, a gross body is still required as an instrument for enjoyment. The gross body may change, but the subtle body continues to act. Unless the living entity gets another gross body, he will have to continue in a subtle body, or a ghostly body. One becomes a ghost when thesubtle body acts without the help of the instrumental gross body. As stated in this verse, śayānam imam utsṛjya śvasantam. The gross body may lie on a bed and rest, and even though the machinery of the gross body is working, the living entity may leave, go into a dream, and return to the gross body.
(Srimad Bhagavatam----4:29:61----purport).

The conclusion is that the subtle body—mind, intelligence and ego—creates an atmosphere with desires and ambitions that the living entity enjoys in the subtle body. Actually the living entity is in the subtle body, even though the gross body apparently changes and even though he inhabits the gross body on various planets. All the activities performed by the living entity in the subtle body are called illusory because they are not permanent. Liberation means getting out of the clutches of the subtle body. Liberation from the gross body simply involves the transmigration of the soul from one gross body to another. When the mind is educated in Kṛṣṇa consciousness, or higher consciousness in the mode of goodness, one is transferred either to the upper, heavenly planets or to the spiritual world, the Vaikuṇṭha planets. One therefore has to change his consciousness by cultivating knowledge received from Vedic instructions from the Supreme Personality of Godhead through the disciplic succession. If we train the subtle body in this life by always thinking about Kṛṣṇa, we will transfer to Kṛṣṇaloka after leaving the gross body. This is confirmed by the Supreme Personality of Godhead.
(Srimad Bhagavatam----4:29:61----purport).

As long as one is absorbed in the bodily conception, his activities are performed on that platform. This is not very difficult to understand. In the world, we see that every nation is trying to supersede every other nation and that every man is trying to advance beyond his fellow man. All these activities are going on under the name of advancement of civilization. There are many plans for making the body comfortable, and these plans are carried in the subtle body after the destruction of the gross body. It is not a fact that after the gross body is destroyed the living entity is finished. Although many great philosophers and teachers in this world are under the impression that after the body is finished everything is finished, this is not a fact.
(Srimad Bhagavatam----4:29:62----purport).

Karma is the aggregate of fruitive activities conducted to make this body comfortable or uncomfortable. We have actually seen that when one man was about to die he requested his physician to give him a chance to live four more years so that he could finish his plans. This means that while dying he was thinking of his plans. After his body was destroyed, he doubtlessly carried his plans with him by means of the subtle body, composed of mind, intelligence and ego. Thus he would get another chance by the grace of the Supreme Lord, the Supersoul, who is always within the heart.
(Srimad Bhagavatam----4:29:62----purport).

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. That is the nature of the mind—thinking, feeling and willing. As long as the mind is not engaged in meditation on the lotus feet of the Supreme Personality of Godhead, Kṛṣṇa, the mind will desire so many material enjoyments. Sensual images are recorded in the mind in chronological order, and they become manifest one after another; therefore the living entity has to accept one body after another.
(Srimad Bhagavatam----4:29:68----purport).

The desires in the subtle body of mind, intelligence and ego cannot be fulfilled without a gross body composed of the material elements earth, water, air, fire and ether. When the gross material body is not manifest, the living entity cannot factually act in the modes of material nature. In this verse it is clearly explained that the subtle activities of the mind and intelligence continue due to the sufferings and enjoyments of the living entity's subtle body. The consciousness of material identification (such as "I" and "mine") still continues because such consciousness has been extant from time immemorial. However, when one transfers to the spiritual world by virtue of understanding Kṛṣṇa consciousness, the actions and reactions of both gross and subtle bodies no longer bother the spirit soul.
(Srimad Bhagavatam----4:29:70----purport).