Why is there no  end to our miseries? Why  can we not experience everlasting happiness? The  answer is simple – a  lack of some basic understanding.
We  still remain ignorant of the very things that  truly need to be  known. For example, we   do not understand the difference between the  perishable and the eternal.  We are unable to discriminate between that  which has a beginning and that which  has been since eternity. We are  unable to differentiate between that which has  an end and that which  does not.
Moreover,  whatever we do know is in fact only partial knowledge. We do  not understand it  properly and fully as it is. On obtaining basic  information, we feel that we  have gained complete knowledge of the  matter. We do not even have the patience  to attain complete knowledge.
Furthermore,  sometimes false knowledge is believed to be true  knowledge. For example, we  believe that which is not the atma to be the  atma. That which causes misery has  started to seem pleasurable. The  sources of true happiness have become unknown  to us. We have taken a  likening to uncertainty and want to settle in it. We  believe the  perishable to be eternal, and we do not accept that which is truly   eternal to be so. Only physical enjoyment is accepted by the mind. We  cannot  rise above logic; we firmly believe that it is impossible to do  so. As a result  of this, we remain engrossed in our bodies and  everything related to them. We  have become comfortable in them. Now we  do not want to leave them. We do not  even think about leaving them.  Talks of the body being perishable seem useless.
In this way, our  ignorance, incomplete knowledge and false beliefs are  the roots of our misery,  but we do not realize this. Instead we cry for  sympathy saying that there is no  end to our miseries and that a cloud  of problems constantly looms above our  heads.
This is our  current situation. But this situation is not permanent, it  can be changed,  there is no doubt about it. We can experience this on  contemplating on the  precepts of the Bhagavad Gita.
SANKHYA JNAN
With the words,  ‘Klaibyam mã sma gamaha pãrtha’ – ‘O Parth, do not be a  coward’ (Gita 2.3).  Krishna, Parth’s charioteer, gave him a dose of  courage. But without a little  understanding, talks of courage alone  cannot win the fight. Only in an  intellect which has mature  understanding does courage gain the stamina to  spread its influence.  Therefore, Shri Krishna then decides to give an  understanding of some  basic, philosophical principles.
This explanation  is known as sankhya jnan. ‘Sankhya’ means true and  complete. Here, sankhya jnan  has been presented to Arjuna by  clarification on what is atma and what is not.
THE DIFFERENCE  BETWEEN THE BODY AND THE ATMA
“Who are you?”  Bhagwan Swaminarayan asked a young boy.
“A Harijan,” the  boy replied, referring to his caste.
“No, you are not  a Harijan, you are atma. Now say ‘I am atma’ ” said  Bhagwan Swaminarayan,  explaining the boy’s true identity to him.
“I am atma,”  repeated the boy obediently.
Bhagwan  Swaminarayan was pleased, yet to verify, he once again asked, “Who are you?”
“A Harijan.”
“No, not a  Harijan, you are atma. Therefore say ‘I am the atma’ ” Bhagwan Swaminarayan  again instructed him.
The boy did so.
“Now, who are  you?” asked Bhagwan Swaminarayan
“A Harijan,” came  the reply.
Then Bhagwan Swaminarayan  made the boy said ‘I am atma’ a hundred  times. The boy had the sentence  memorized. Finally Bhagwan Swaminarayan  asked, “Who are you?” The boy said,  “Because you say so, I am atma,  but, in reality, I am a Harijan.’
This is the  result of believing oneself to be the body.
It is obvious  that a person living in a house is separate  from the house. No one says that  the owner of a chariot and the chariot  itself are one. Everyone knows that a  bird is separate from its cage.  The same applies to the atma and the body, yet  we find it hard to  understand. Why? The reason is our belief that we are the  body.
This belief is  the king of all ignorances. To believe one’s  body to be the atma is known as  dehatmabhav. This is a type of madness  that can be compared with someone living  in a house believing himself  to be the house. This is the pitiful situation of  a bird who believes  itself to be the cage. Since time eternal, such a false  understanding  has taken firm control over us, and we have become accustomed to  being  its slave.
Therefore,  today’s most urgent need is a change of control.  We must be courageous. The  only choice is to discard this belief of  being the body and realize the true  knowledge of one’s atma. There is  no room for feelings of inferiority or  cowardice in this matter. The  Gita teaches us how to develop this control of  atmajnan in a simple  manner.
Although Arjuna  is in fact brave, he has been attacked by  cowardice born from dehbhav  (believing one’s true self to be the body).  He has therefore suffered a decline  and is confused. Shri Krishna now  teaches him the method of getting the atma  into power. First of all,  with simple analogies, he explains how the body and  atma are separate  in form and entity.
Shri Krishna  Bhagwan says, ‘देहिनोऽस्मिन् यथा देहे कौमारं यौवनं जरा। तथा देहान्तरप्राप्तिर्घीरस्तत्र  न मुह्यति॥’ – ‘Dehino’smin yathã dehe kaumãram yauvanam jarã, tathã  dehãntaraprãptirdheerastatra na muhyati.’    – ‘Just like the atma, which is the controller of the body, passes   through the stages of childhood, young age and old age in this body, it   similarly attains other bodies as well, the wise are not distraught by  this’  (Gita 2.13).
Here, the words  ‘Dehino’smin yathã dehe’ clearly show that  the deha – body, and the dehi that  which resides in the body, the atma,  are distinct from each other. Our bodies  change, but our atma does  not. This difference has been shown here with the  principle of  punarjanma. The analogy given is of the changes that take place in  our  bodies. The body is born and the rise and fall of various stages  commences.  Childhood begins and slowly diminishes as adolescence sets  in. Before we even  know it, old age eclipses the radiance of our youth,  and finally death swallows  old age. This cycle of change is  continuous, but in this cycle of change, the  atma remains the same.  When we are reborn, a new atma is not born, but the same  atma that was  in the previous body attains a new body.
Krishna implies,  ‘O Arjuna! It is just as natural to obtain  a new birth as it is to pass through  the phases of childhood, youth  and old age. You are courageous, but now become  wise too. Do not grieve  on seeing the bodies of your relatives die opposite you  in war.’
Krishna then  gives another analogy. ‘वासांसि जीर्णानि यथा विहाय नवानि गृह्णाति नरोऽपराणि। तथा  शरीराणि विहाय जीर्णान्यन्यानि संयाति नवानि देही॥’ ‘Vãsãnsi jeernãni yathã  vihãya navãni gruhnãti naro’parãni, tathã shareerãni vihãya jeernãnyanyãni  samyãti navãni dehee.’  – ‘Just like a person throws away old clothes and adorns  new ones,  similarly, the dehi, i.e., the atma, that resides in this body,  leaves  an old body and attains a new one’ (Gita 2.22).
Krishna has given  an analogy of something as natural as  changing our clothes, a daily process. No  one believes themselves to be  their clothes, and if they do, they are  considered mad. The body is  just a cloth, and the atma, distinct from the  cloth, is one who wears  it. We should also take a look at these words from a  grammatical point  of view. ‘Naraha’(person) and ‘dehee’ (body) are both  singular, whereas  ‘vasansi’ (clothes) and ‘shareerani’ (bodies) are both  plural.  Therefore just as a single person adorns many clothes one after   another, similarly a single atma attains many bodies one after the  other.
Parabrahman  Purushottam Bhagwan Swaminarayan has mentioned  the same point with a different  perspective. A Brahmin named Vala Dhruv  of the village Vaso asked Bhagwan  Swaminarayan, “Maharaj, how can the  feelings of I-ness and my-ness towards  one’s body and its relations be  eradicated?”
Shriji Maharaj  replied, “The jiva has a misconception in  that it does not believe itself to be  the jivatma, i.e., distinct from  the body; instead, it believes itself to be  the body. To illustrate how  the body clings to the jivatma, consider a person  who wears a dagli  after having it sewn by a tailor. That person then begins to  believe,  ‘The tailor is my father and the tailor’s wife is my mother.’ Such a   person would be considered a fool. In the same manner, the jivatma is  given a  dagli in the form of this body, which is born sometimes to a  Brahmin couple;  sometimes to a low-caste couple; or in any of the 8.4  million life forms.  Therefore, a person who believes the body to be his  true self and believes the  parents of that body to be his own parents  is called a fool,… Therefore, as  long as a person believes the body to  be his true self, his entire  understanding is totally useless”  (Vachanamrut, Gadhada I 44).
Shri Krishna  Bhagwan explains the difference between the body and the atma to Arjuna saying,  ‘अन्तवन्त इमे देहा नित्यस्योक्ताः शरीरिणः। अनाशिनोऽप्रमेयस्य तस्माद् युद्ध्यस्व  भारत॥’ – ‘Antavanta ime dehã nityasyoktãhã shareerinaha, anãshino’prameyasya  tasmãd yuddhyasva Bhãrata.’ – ‘O Arjuna, the bodies of this indestructible  imperishable eternal atma are destructible, therefore fight’ (Gita 2.18).
One is  destructible, the other indestructible. He shows their diversity by  highlighting their inherent qualities. 
He also gives a  detailed explanation of the form of the atma.