In the Fifteenth Chapter of the Bhagavad-gita, the real picture of the material world is given. It is said there:

Urdhva-mulam adhah-sakham
Asvattham prahur avyayam
Chandamsi yasya parnani
Yas tam veda sa veda-vit

Here the material world is described as a tree whose roots are upwards and branches are below. We have experience of a tree whose roots are upward: if one stands on the bank of a river or any reservoir of water, he can see that the trees reflected in the water are upside down. The branches go downward and the roots upward. Similarly, this material world is a reflection of the spiritual world. The material world is but a shadow of reality. In the shadow there is no reality or substantiality, but from the shadow we can understand that there are substance and reality. In the desert there is no water, but the mirage suggests that there is such a thing as water. In the material world there is no water, there is no happiness, but the real water of actual happiness is there in the spiritual world.

The Lord suggests that we attain the spiritual world in the following manner (Bg. 15.5):

Nirmana-moha jita-sanga-dosa
Adhyatma-nitya vinivrtta-kamah
Dvandvair vimuktah Sukha-duhkha-samjnair
Gacchanty amudhah padam avyayam tat

That padam avyayam, or eternal kingdom, can be reached by one who is nirmana-moha. What does this mean? We are after designations. Someone wants to become “sir,” someone wants to become “lord,” someone wants to become the president or a rich man or a king or something else. As long as we are attached to these designations, we are attached to the body, because designations belong to the body. But we are not these bodies, and realizing this is the first stage in spiritual realization. We are associated with the three modes of material nature, but we must become detached through devotional service to the Lord. If we are not attached to devotional service to the Lord, then we cannot become detached from the modes of material nature. Designations and attachments are due to our lust and desire, our wanting to lord it over the material nature. As long as we do not give up this propensity of lording it over material nature, there is no possibility of returning to the kingdom of the Supreme, the sanatana-dhama. That eternal kingdom, which is never destroyed, can be approached by one who is not bewildered by the attractions of false material enjoyments, who is situated in the service of the Supreme Lord. One so situated can easily approach that supreme abode.

Elsewhere in the Gita (8.21) it is stated:

Avyakto ksara ity uktas
Tam ahuh paramam gatim
Yam prapya na nivartante
Tad dhama paramam mama

Avyakta means unmanifested. Not even all of the material world is manifested before us. Our senses are so imperfect that we cannot even see all of the stars within this material universe. In Vedic literature we can receive much information about all the planets, and we can believe it or not believe it. All of the important planets are described in Vedic literatures, especially Srimad-Bhagavatam, and the spiritual world, which is beyond this material sky, is described as avyakta, unmanifested. One should desire and hanker after that supreme kingdom, for when one attains that kingdom, he does not have to return to this material world.

Next, one may raise the question of how one goes about approaching that abode of the Supreme Lord. Information of this is given in the Eighth Chapter. It is said there:

Anta-kale ca mam eva
Smaran muktva kalevaram
Yah prayati sa mad-bhavam
Yati nasty atra samsayah

“Anyone who quits his body, at the end of life, remembering me, attains immediately to My nature; and there is no doubt of this.” (Bg. 8.5) One who thinks of Krishna at the time of his death goes to Krishna. One must remember the form of Krishna; if he quits his body thinking of this form, he surely approaches the spiritual kingdom. Mad-bhavam refers to the supreme nature of the Supreme Being. The Supreme Being is sac-cid-ananda-vigraha – that is, His form is eternal, full of knowledge and bliss. Our present body is not sac-cid-ananda. It is asat, not sat. It is not eternal; it is perishable. It is not cit, full of knowledge, but it is full of ignorance. We have no knowledge of the spiritual kingdom, nor do we even have perfect knowledge of this material world, where there are so many things unknown to us. The body is also nirananda, instead of being full of bliss it is full of misery. All of the miseries we experience in the material world arise from the body, but one who leaves this body thinking of Lord Krishna, the Supreme Personality of Godhead, at once attains a sac-cid-ananda body.

The process of quitting this body and getting another body in the material world is also organized. A man dies after it has been decided what form of body he will have in the next life. Higher authorities, not the living entity himself, make this decision. According to our activities in this life, we either rise or sink. This life is a preparation for the next life. If we can prepare, therefore, in this life to get promotion to the kingdom of God, then surely, after quitting this material body, we will attain a spiritual body just like the Lord’s.

As explained before, there are different kinds of transcendentalists – the brahma-vadi, param-atma-vadi and the devotee-and, as mentioned, in the brahmajyoti (spiritual sky) there are innumerable spiritual planets. The number of these planets is far, far greater than all of the planets of this material world. This material world has been approximated as only one quarter of the creation (ekamsena sthito jagat). In this material segment there are millions and billions of universes with trillions of planets and suns, stars and moons. But this whole material creation is only a fragment of the total creation. Most of the creation is in the spiritual sky. One who desires to merge into the existence of the Supreme Brahman is at once transferred to the brahmajyoti of the Supreme Lord and thus attains the spiritual sky. The devotee, who wants to enjoy the association of the Lord, enters into the Vaikuntha planets, which are innumerable, and the Supreme Lord by His plenary expansions as Narayana with four hands and with different names like Pradyumna, Aniruddha and Govinda associates with him there. Therefore at the end of the life the transcendentalists think either of the brahmajyoti, the Paramatma or Supreme Personality of Godhead Sri Krishna. In all cases they enter into the spiritual sky, but only the devotee, or he who is in personal touch with the Supreme Lord, enters into the Vaikuntha planets or the Goloka Vrindavana Planet. The Lord further adds that of this “there is no doubt.” This must be believed firmly. We should not reject that which does not tally with out imagination; our attitude should be that of Arjuna: “I believe everything that You have said.” Therefore when the Lord says that at the time of death whoever thinks of Him as Brahman or Paramatma or as the Personality of Godhead certainly enters into the spiritual sky, there is no doubt about it. There is no question of disbelieving it.”

The Bhagavad-gita (8.6) also explains the general principle that makes it possible to enter the spiritual kingdom simply by thinking of the Supreme at the time of death:

Yam yam vapi smaran bhavam
Tyajaty ante kalevaram
Tam tam evaiti kaunteya
Sada tad-bhava-bhavitah

“Whatever state of being one remembers when he quits his present body, in his next life he will attain to that state without fail.” Now first we must understand that material nature is a display of one of the energies of the Supreme Lord. In the Vishnu Purana (6.7.61) the total energies of the Supreme Lord are delineated:

Vishnu-saktih para prokta
Kshetra jnakhya tatha para
Avidya-karma-samjnanya
Trtiya saktir isyate

The Supreme Lord has diverse and innumerable energies which are beyond our conception; however, great learned sages or liberated souls have studied these energies and have analyzed them into three parts. All of the energies are of Vishnu-Shakti, that is to say they are different potencies of Lord Vishnu. The first energy is para, transcendental. Living entities also being to the superior energy, as has already been explained. The other energies, or material energies, are in the mode of ignorance. At the time of death either we can remain in the inferior energy of this material world, or we can transfer to the energy of the spiritual world. So the Bhagavad-gita (8.6) says:

Yam yam vapi smaran bhavam
Tyajaty ante kalevaram
Tam tam evaiti kaunteya
Sada tad-bhava-bhavitah

“Whatever state of being one remembers when he quits his present body, in his next life he will attain to that state without fail.”

In life we are accustomed to thinking either of the material or of the spiritual energy. Now, how can we transfer our thoughts from the material energy to the spiritual energy? There are so many literatures which fill our thoughts with the material energy – newspapers, magazines, novels, etc. Our thinking, which is now absorbed in these literatures, must be transferred to the Vedic literatures. The great sages, therefore, have written so many Vedic literatures, such as the Puranas. The Puranas are not imaginative; they are historical records. In the Chaitanya-caritamrta (Madhya 20.122) there is the following verse:

Maya-mugdha jivera nahi svatah Krishna-jnana
Jivere krpaya kaila Krishna veda-purana

The forgetful living entities or conditioned souls have forgotten their relationship with the Supreme Lord, and they are engrossed in thinking of material activities. Just to transfer their thinking power to the spiritual sky, Krishna-dvaipayana Vyasa has given a great number of Vedic literatures. First he divided the Vedas into four, then he explained them in the Puranas, and for less capable people he wrote the Mahabharata. In the Mahabharata there is given the Bhagavad-gita. Then all Vedic literature is summarized in the Vedanta-sutra, and for future guidance he gave a natural commentation on the Vedanta-sutra called Srimad-Bhagavatam. We must always engage our minds in reading these Vedic literatures. Just as materialists engage their minds in reading newspapers, magazines and so many materialistic lieteratures, we must transfer our reading to these literatures, which are given to us by Vyasadeva; in that way it will be possible for us to remember the Supreme Lord at the time of death. That is the only way suggested by the Lord, and He guarantees the result: “There is no doubt.”

Tasmat sarvesu kalesu
Mam anusmara yudhya ca
Mayy arpita-mano-buddhir
Mam evaisyasy asamsayah

“Therefore, Arjuna, you should always think of Me in the form of Krishna and at the same time continue your prescribed duty of fighting. With your activities dedicated to Me and your mind and intelligence fixed on Me, you will attain me without doubt.” (Bg. 8.7)

He does not advise Arjuna simply to remember Him and give up his occupation. No, the Lord never suggests anything impractical. In this material world, in order to maintain the body one has to work. Human society is divided, according to work, into four divisions of social order – Brahmana, Kshatriya, vaishya and sudra. The Brahmana class or intelligent class is working in one way, the Kshatriya or administrative class is working in another way, and the mercantile class and the labourers are all tending to their specific duties. In the human society, whether one is a labourer, merchant, administrator or farmer, or even if one belongs to the highest class and is a literary man, a scientist or a theologian, he has to work in order to maintain his existence. The Lord therefore tells Arjuna that he need not give up his occupation, but while he is engaged in his occupation he should remember Krishna (mam anusmara). If he doesn’t practice remembering Krishna while he is struggling for existence, then it will not be possible for him to remember Krishna at the time of death. Lord Chaitanya also advises this, He says, kirtaniyah sada harih: one should practice chanting the names of the Lord always. The names of the Lord and the Lord are nondifferent. So Lord Krishna’s instructions to Arjuna to “remember Me” and Lord. Chaitanya’s injunction to “always chant the names of Lord Krishna” are the same instruction. There is no difference, because Krishna and Krishna’s name are nondifferent. In the absolute status there is no difference between reference and referent. Therefore we have to practice remembering the Lord always, twenty-four hours a day, by chanting His names and molding our life’s activities in such a way that we can remember Him always.