In Gurbani the definition of ego is as under:

" The personality of ego is such that its influence one acts in pride.
The trammel of ego makes one enter into existences again and again.
From where is the ego born and by what method can it be removed?
This (ego) is Lord's will and on account of ego one wanders (comes into existences) according to past acts.
Ego is a chronic disease, but it is curable. If the Lord bestows His grace then one acts according the Guru's instruction( and this is the cure for ego).
Says Nanak, hear O' Ye people, in this way this disease (of ego) is cured."
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So ego means that man, under its influence, considers himself a separate entity (from the Lord) and to preserve it he acts according to his own will and in this manner goes on increasing his ego. Whatever action he does under the influence of this desire (of preserving his entity) due to those actions he is caught in the trammel.

Gurbani says:

"Whatever deeds on does, attached with avarice, with tem all one binds himself down. Pause."
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Such actions bind the soul and make her come into existences again and again and the soul remains in the circle of death and birth. So long as the soul remains in unison with God, she remains happy and when the soul considered herself a separate entity and to preserve that separate entity she acts and does deeds, those deeds bind the soul and the circle of death and birth continues. This circle of death and birth continues till the perverse soul does not achieve unison, after destroying her ego, with God.

What deeds the soul does under the influence of ego? The answer it this question has been given by Shri Guru Nanak Dev as under:

"In pride (ego) man comes and in pride he departs.
In pride he is born and in pride he dies.
In pride he gives (becomes a gifter) and in pride he takes (becomes a beggar).
In pride he earns and in pride he looses.
In pride he becomes true (speaks truth) or false (speaks lies).
In pride he reflects on virtue or vice.
In pride he falls in hell or heaven.
In pride he laughs and in pride he weeps.
In pride he is soiled and in pride he washes (himself of sins).
In pride he enters into different castes and species.
In pride he becomes ignorant and in pride he becomes wise. He does not know the worth of salvation and emancipation.
In pride he loves and in pride he is shadowed by it.
Due to pride the beings are created. If ego (pride) is stilled then the soul experiences God and becomes one with Him.
Without divine knowledge man prattles, prattles and wrangles.
Nanak, under the Lord's order (which is according to the deeds of a soul)) the destiny of a soul is recorded. And a man becomes good or bad according to his actions."
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The following question was put to Shri Guru Angad Dev:

Sir, from where this ego is born and by what means and methods can it be destroyed? He replied "Brother, ego has been created under God's will. Under its influence the soul, according to its deeds comes into existences and remains in the circle of death and birth. Ego is a chronic disease but the creator has also created medicine for it. The medicine is that if the Lord bestows His grace then the egoistic man starts acting on the Guru's instructions. Nanak says, Hear, O' ye people in this way ego is destroyed."

Shri Guru Nanak Dev says that whosoever created a separate entity (from the Lord) he is caught in the trammel of ego. He further says:

"Remember this O' Nanak that whosoever says ' I AM', he is bound down. I have no ego and self conceit and so will not come into existence again i.e. will not be reborn. So, silly soul destroy your ego. This is the best virtue out of all the virtues.
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Gurbani says:

"O' ignorant man, destroy your egoistic thoughts. Still your egos, meditate on God in your heart, and in you mind gather the virtues (of the virtues Lord) and this is the best virtue. Pause."
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So long as the soul does not destroy its ego it cannot achieve unison with the Lord. It means that the destruction of ego leads to unison with the Lord and the soul obtains her beloved who is owner of all the nine treasures.

Gurbani says:

"If the soul effaces her ego then she merges in her spouse and then alone can the bride (soul) obtain her beloved who Himself is all the nine treasures;"
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Shri Guru Amar Dass:

"Nanak NAM abides in the mind when self-Conceit is eradicated."
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To explain this Gurbani says:

"Ego is as variance with NAM, the two do not dwell in one place."
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Unison with God is not possible through intellect or cleverness. Gurbani says:

"Efface your self conceit and then you will obtain the Groom. Of what avail are other clevernesses."
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The believers once asked Shri Guru Arjan Dev to tell them the method of achieving unison with God. He replied as under:

"Listen, O' mate, I tell you the way to meet the Lord. Still your entire self-conceit (ego) then you will find your Beloved in your mind itself."
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To other such questions, Shri Guru Arjan Dev has replied as under:

"Show me the path, O' saints, as to how can I meet my Lord?
Dedicate your mind and renounce your ego. This is the path along which you should walk."
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This is only way to achieve unison with God. The soul who wants to achieve unison with God asks another realised soul the method of achieving unison with God. This question has been answered in Gurbani as under:

"I go and ask the fortunate faithful bride as to how you obtained the Groom, my Lord."

She answered:

"I abandoned the differentiation between mine and thine and the True Spouse blessed me with his mercy.
Surrender your mind, body, soul and all to the Lord God. This is the way to meet Him, O' my sister.
Nanak if the Lord beholds the mind then man's Light blends with God's Light."
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This quotation clarifies that Lord's grace is conditioned. To obtain Grace man has to make efforts. He has to surrender his body, mind, soul and all to Lord God, only then He bestows His Grace, and not otherwise. Perverse minds and sinners often say that we would achieve unison with God if He casts Graceful glance as without His Grace nothing can be achieved. They should carefully examine the above principles laid down by the Guru. There is no doubt that without grace NAM cannot be obtained but to get His Grace the above instructions of Guru have to be complied with.

It has been enunciated clearly that so long a ego exists NAM cannot be experienced. Given below are who means and methods, which have to be complied with to experience NAM. Gurbani says:

"Through fascinating mammon wells up ego and man is yoked to duality. It (ego) cannot be slain nor can it be sold off at a shop. It (ego) departs from within only if man burns it off through the WORD (Gurbani).
Then his body and soul become immaculate and NAM abides in his mind.
O' Nanak, the WORD (Gurbani) is the destroyer of mammon but this WORD is achieved through the Guru i.e. by obeying His instructions."
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In the above quotation the method of destroying ego has been explained. When with the WORD of the Guru ego is burned then NAM abides in the mind. Now the question arises what is the WORD of the Guru. When this question was put to Guru Arjan Dev, he replied as under:

"May my worldly love and sense of 'mine' and 'thine' be removed and my self-conceit be destroyed.
O' Saints, tell me the method by which my self-conceit and ego may be banished. Pause."
I experience the supreme Lord everywhere and so I feel like the dust of the feet of all. I see the Lord ever with me and the wall of my doubt (ego) has been shattered."

The method has been clearly enunciated in the last lines of the above quotations. One should always remember that to experience His presence the wall of doubt, ego has to be removed and one must remember:

"By singing God's glories the filth (of attachment) shall be washed off and the all spreading poison of ego shall depart."
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So the only method of destroying ego is that the man should sing praises of the Lord, with complete faith that the Boundless, Greatest Lord is All-pervading and is nearest to him. In this manner, the chronic disease of ego is destroyed.