Substance of Bhagavadgita in brief

The experience of happiness and distress in life are like the appearance and disappearance of winter and summer seasons,  tolerate them without being disturbed.

For the soul, there is neither birth nor death nor it cannot be destroyed. It is everlasting and imperishable. He who dwells in the body is eternal and can never be killed. 

Why you cry that you may lose something.? What did you bring with you, which you think you are losing now? What did you create your own,  which you think now that it is being destroyed? 

You came with empty hands, you will leave with empty hands only.  Whatever is going to happen will definitely happen.  It is God's will. Don't worry about it unnecessarily

Be like a sage, who is not disturbed in spite of miseries nor delighted when there is happiness, free from attachment, fear, and anger. Be free from desires, devoid of false ego, and then alone you attain Real Happiness.

Do your prescribed duty for the sake of God and free from bondage. You should do your karma without being idle. Whatever be the result you must accept it as a divine blessing. Time is valuable. Don't waste it. It won't come back again.

Do not addict to material pleasures, they will entrap you in material miseries. Do the good deeds immediately, without postponing them. Keep ego, jealousy, and greed away from your thoughts. Keep your mind pure, adore humanity as your crown and live a pious life. Love all beings as the creation of God and try to establish Peace in the Universe.

In the course of performing one's own Dharma, death is better than engaging in another's Dharma.  To follow others' Dharma(Path)  is dangerous.

Whatever you do,  do it as a dedication to God. This will bring you the tremendous experience of joy and life freedom forever. 

One who performs his duty without attachment, surrendering the result unto the Supreme God is not affected by sinful action, as the lotus leaf is untouched by water.

If one eats too much or eats too little, sleeps too much, or does not sleep enough, there is no possibility of becoming a Yogi.  A perfect Yogi who by comparison to his own self sees the true equality of all beings both in their happiness and distress.

Don't dwell in delusion, overcome by the dualities of desire and hate.

Take the spiritual world to enjoy eternal life full of bliss and knowledge and never return to this miserable material existence.

If one offers Me with love and devotion, a leaf, a flower, a fruit, or water, I  will accept it.

All that you do, all that you eat, all that you offer and give away, as well as all austerities that you may perform, should be done as an offering unto Me and by this principle of renunciation, you will be liberated and come to Me.

In devotional services, there is no distinction between lower or higher classes viz., Brahmana, Kshatriya, Vysya and Sudra. One who is not envious but who is kind to all living entities, who does not think himself an owner, who is free from false ego and equal both in distress and happiness, who is always satisfied and engaged in devotional services with determination and whose mind and intelligence are in agreement with Me, not disturbed by anxiety, free from all pains, does not strive for some result, who renounces both auspicious and inauspicious things, equal to friends and enemies, honour and dishonour, heat and cold, fame and infamy, engaged in devotional services, completely engages himself with faith, making Me the supreme goal is very very dear to Me.

The living entity even though situated in various bodies is aloof from them, due to its subtle nature, and it is out of it after the destruction of the body.

When the mode of passion is increased one develops the hankering for material enjoyment.  He wants to enjoy sense gratification.  For this, a man in the mode of passion wants some honour in the society, a happy family, nice children, wife and house.

If one develops the mode of ignorance, after his death, he is degraded to the animal form of life.

By acting in the mode of goodness one becomes purified and real knowledge develops.

Works were done in the mode of passion, result in distress and grief develops and actions performed in the mode of ignorance result in foolishness, madness, and illusion develops.

When one is freed from the influence of the modes of material nature he enters into devotional service.

One who is free from illusion, false prestige and false association,  who understands the eternal, who is done with material lust and is freed from the duality of happiness and distress, and who knows how to surrender unto the Supreme Person attains to that Eternal Kingdom,

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In each and every individual body the fragmental portion of the Supreme Lord is present.  That fragmental portion,  when liberates from the bodily entanglement, revives its original spiritual body in the spiritual sky in a spiritual planet and enjoys with the  Supreme Lord.  The living entity is the fragmental part and parcel of the Supreme Lord.

The man who has escapes lust, anger and greed which are the three gates of Hell, performs acts conducive to self-realisation and thus gradually attains the supreme destination.

Acts of sacrifice, charity, and penance are to be performed to purify our souls, performed without any expectation of a result, performed as a matter of duty. One can obtain the results of renunciation simply by self-control and by becoming unattached to material things and disregarding material enjoyments. That is the highest perfectional stage of Renunciation.

When one is purified by knowledge, he keeps himself in the mode of goodness. Thus one becomes the controller of mind and is always in trance.  Because he is not attached to the objects of sense gratification, he does not eat more than what he requires, and he controls the activities of his body and mind.  He has no false ego because he does not accept the body as himself nor has he a desire to make the body fat and strong by accepting so many material things. Because he has no bodily concept of life, he is not falsely proud. He is satisfied with everything that is offered to him by the grace of the Lord and he is never angry in the absence of sense gratification.  Nor does he endeavor to acquire sense objects.

Thus when he is completely free from a false ego, he becomes non-attached to all material things and that is the stage of self-realization of Brahman. When one is free from the material conception of life, he becomes peaceful and cannot be agitated. He never laments nor desires to have anything, he is equally disposed to every living entity.  In that state, he attains pure devotional service UN to Me. And when one is in full consciousness of the Supreme Lord by such devotion he can enter into the kingdom of God. Though engaged in all kinds of activities My devotee under My protection reaches the eternal and imperishable abode of My Grace. 

The Supreme Lord is situated in everyone's heart and is directing the wanderings of all living entities, who are seated as on a machine made by the material energy.

Source from Bhagavat Gita by Sri AC Bhakti Vedantha  Prabhupada Swamiji.