The subject of the Bhagavad-gita entails the comprehension of five basic truths. First of all, the science of God is explained and then the constitutional position of the living entities, jivas. There is ishvara, which means the controller, and there are jivas, the living entities which are controlled. If a living entity says that he is not controlled but that he is free, then he is insane. The living being is controlled in every respect, at least in his conditioned life. So in the Bhagavad-gita the subject matter deals with the ishvara, the supreme controller, and the jivas, the controlled living entities. Prakriti (material nature) and time (the duration of existence of the whole universe or the manifestation of material nature) and karma (activity) are also discussed. The cosmic manifestation is full of different activities. All living entities are engaged in different activities. From Bhagavad-gita we must learn what God is, what the living entities are, what prakriti is, what the cosmic manifestation is, how it is controlled by time, and what the activities of the living entities are.
Ishvara (the Supreme Lord)
Out of these five basic subject matters in Bhagavad-gita it is established that the Supreme Personality of Godhead, or Krishna, or Brahman, or the supreme controller, or Paramatma—you may use whatever name you like—is the greatest of all. The living beings are in quality like the supreme controller. For instance, the Lord has control over the universal affairs of material nature, as is explained in the Bhagavad-gita.
Material nature is not independent. She is acting under the directions of the Supreme Lord. As Lord Krishna says, mayadhyaksena prakrtih suyate sa-caracaram: "This material nature is working under My direction." When we see wonderful things happening in the cosmic nature, we should know that behind this cosmic manifestation there is a controller. Nothing could be manifested without being controlled. It is childish not to consider the controller. For instance, a child may think that an automobile is quite wonderful to be able to run without a horse or other animal pulling it, but a sane man knows the nature of the automobile's engineering arrangement. He always knows that behind the machinery there is a man, a driver. Similarly, the Supreme Lord is the driver under whose direction everything is working.
Jiva (the living entity)
Now the jivas, or the living entities, have been accepted by the Lord, as we will note in the later chapters, 
as His parts and parcels. A particle of GOLD is also gold, a drop of water from the ocean is also salty, and similarly we the living entities, being part and parcel of the supreme controller, ishvara, or Bhagavan,Lord Shri Krishna, have all the qualities of the Supreme Lord in minute quantity because we are minute ishvaras, subordinate ishvaras. We are trying to control nature, as presently we are trying to control space or planets, and this tendency to control is there because it is in Krishna. But although we have a tendency to lord it over material nature, we should know that we are not the supreme controller. This is explained in Bhagavad-gita.
as His parts and parcels. A particle of GOLD is also gold, a drop of water from the ocean is also salty, and similarly we the living entities, being part and parcel of the supreme controller, ishvara, or Bhagavan,Lord Shri Krishna, have all the qualities of the Supreme Lord in minute quantity because we are minute ishvaras, subordinate ishvaras. We are trying to control nature, as presently we are trying to control space or planets, and this tendency to control is there because it is in Krishna. But although we have a tendency to lord it over material nature, we should know that we are not the supreme controller. This is explained in Bhagavad-gita.
Prakriti (nature)
What is material nature? This is also explained in Gita as inferior prakriti, inferior nature. The living entity is explained as the superior prakriti. Prakriti is always under control, whether inferior or superior. Prakrti is female, and she is controlled by the Lord just as the activities of a wife are controlled by the husband. Prakriti is always subordinate, predominated by the Lord, who is the predominator. The living entities and material nature are both predominated, controlled by the Supreme Lord. According to the Gita, the living entities, although parts and parcels of the Supreme Lord, are to be considered Prakriti. This is clearly mentioned in the Seventh Chapter of Bhagavad-gita. Apareyam itas tv anyam prakrtim viddhi me param/ jiva-bhutam: "This material nature is My inferior prakriti, but beyond this is another prakriti - jiva-bhutam, the living entity.
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Kala (eternal time)
Another name of the Paramatma feature of the Lord is kala, or eternal time. Eternal time is the witness of all our actions, good and bad, and thus resultant reactions are destined by Him. Paramatma is our constant companion, and therefore He knows everything, past, present and future. And because the Paramatma feature of Lord Krishna destines all actions and reactions, He is the supreme controller also. Without His sanction not a blade of grass can move. The living beings are given as much freedom as they deserve, and those who misuse freedom, are put into miseries destined by the eternal kala. The kala offers the conditioned souls both happiness and miseries. It is all predestined by eternal time. As we have miseries uncalled-for, so we may have happiness also without being asked, for they are all predestined by kala. Everyone is suffering and enjoying the result of his own destiny. This destiny is made by the living beings in course of social intercourse. And because the Lord has no beginning or end, He is known also as the eternal time, kala.
Karma (activity)
Material nature itself is constituted by three qualities: the mode of goodness, the mode of passion and the mode of ignorance. Above these modes there is eternal time, and by a combination of these modes of nature and under the control and purview of eternal time there are activities, which are called karma. These activities are being carried out from time immemorial, and we are suffering or enjoying the fruits of our activities. For instance, suppose there is a businessman and he has worked very hard with intelligence and has amassed a great bank balance. Then he is an enjoyer. But then say he has lost all his MONEY in business; then he is a sufferer. Similarly, in every field of life we enjoy the results of our work, or we suffer the results. This is called karma.
Eternal and non-eternal
Ishvara (the Supreme Lord), jiva (the living entity), prakriti (nature), kala (eternal time) and karma (activity) are all explained in the Bhagavad-gita. Out of these five, the Lord, the living entities, material nature and time are eternal. The manifestation of prakriti may be temporary, but it is not false. Some philosophers say that the manifestation of material nature is false, but according to the philosophy of Bhagavad-gita or according to the philosophy of the Vaishnavas,this is not so. The manifestation of the world is not accepted as false; it is accepted as real, but temporary. It is likened unto a cloud which moves across the sky, or the coming of the rainy season, which nourishes grains. As soon as the rainy season is over and as soon as the cloud goes away, all the crops which were nourished by the rain dry up. Similarly, this material manifestation takes place at a certain interval, stays for a while and then disappears. Such are the workings of prakrti. But this cycle is working eternally. Therefore prakrti is eternal; it is not false. The Lord refers to this as "My prakrti." This material nature is the separated energy of the Supreme Lord, and similarly the living entities are also the energy of the Supreme Lord, although they are not separated but eternally related. So the Lord, the living entity, material nature and time are all interrelated and are all eternal. However, the other item, karma, is not eternal. The effects of karma may be very old indeed. We are suffering or enjoying the results of our activities from time immemorial, but we can change the results of our karma, or our activity, and this change depends on the perfection of our knowledge. We are engaged in various activities. Undoubtedly we do not know what sort of activities we should adopt to gain relief from the actions and reactions of all these activities, but this is also explained in the Bhagavad-gita.
"Chant Hare Krishna and be happy"हरे कृष्ण हरे कृष्ण कृष्ण कृष्ण हरे हरे || हरे राम हरे राम राम राम हरे हरे||
