Bhagavad-gita  also describes how one should act in order to enter into the spiritual kingdom. Material Nature is a display of one of the energies of the Supreme Lord. In the  Visnu Purana , the energies of the Supreme Lord have been summarized. The Lord has diverse, innumerable energies, of which we cannot conceive. But great learned souls have summarized all of these energies into three categories: The first is the superior, or internal, potency of the Lord. That energy is transcendental. Next is the marginal energy, which lies between the spiritual and the material. Originally, all the living entities belong to the eternal superior energy. The third energy, matter, is in the mode of ignorance. Material energy is also from God. And we can, at death, either leave this material world or remain here. Therefore, we are called marginal.
We are accustomed to think in terms of material energy. How can we transfer our thinking of material energy into thinking of spiritual energy? There is so much literature of the material world, like novels, newspapers, etc. We must transfer our reading from these to the spiritual Vedic literature. The learned sages wrote a great deal of literature, like the  Puranas . In  Caitanya-caritamrta  there is a verse which reads: “The conditioned souls have forgotten their eternal relationship with the Lord, and are engrossed in thinking of material things. They should just transfer their thinking to the Lord. He has created so many  Vedas  for this purpose.”
At first, there were four  Vedas . Then He explained them by the  Puranas . Then, for those incapable of understanding these, He gave the  Mahabharata , in which there is the  Bhagavad-gita . Then the  Vedanta-stitra , which summarizes all Vedic knowledge. At last, the  Vedanta-satra  was explained in  Srimad-Bhagavatam .
Just as the materialist is always engaged in reading materialistic literature, so the devotee centers his reading capacity in this literature, so kindly presented by Vyasadeva, so that at the time of death the devotee may think of the Lord and go to Him.
Krsna advises Arjuna not simply to go on remembering Him and give up his material duty. The Lord never suggests anything impractical. To maintain the material body, one has to work. The working world is divided into four parts:  brahmana ,  ksatriya ,  vaisya , and  sudra . Each one works in a different way, as learned man, administrator, mercantiler, or laborer. The Lord advises us not to give up work, but to remember Him always, along with the struggle for existence. This is Krsna consciousness. Unless one does this, it is not possible to go to the Lord.