Vishnu Sahasranama Stotra is part of the Mahabharata. It appears in the Anushasana Parva of the Mahabharata.
Mahabharata has 18 sections called Parvas. Out of these, the 12th and 13th, Shanti Parva and Anushasana Parva, deal with dharma, such as the duties of the king, what is good governance, and how men and women should conduct themselves.
They are in the form of discussions and question-answers between Bhishma, various rishis, and Yudhishthira. This is after the war is over.
Bhishma is on shara shayya, the bed made of arrows, his deathbed. He was chiranjeevi, and he would die only at his own will. He opted to end his life. He was waiting for an auspicious time to leave the body.
Adi Shankaracharya in Bhaja Govindam says, "Geyam Geeta Nama Sahasram." Sing Bhagavad Gita and Sahasranama.
They are on par with each other.
The ultimate truth is revealed in the Geeta using logic and reasoning.
The same ultimate truth exists in Sahasranama as the thousand names of that ultimate truth.
Geeta should be understood and practiced. There is no substantial benefit by merely learning the Gita by heart or chanting it. Geeta is knowledge; it should be understood, and the understanding strengthened and made into one’s own life by constant practice.
The practice of Geeta is not like a half-an-hour meditation session. You should live the Geeta 24 X 7. That is what Gita is meant for.
Sahasranama is for chanting. You need not even understand the meaning of the thousand names. Still, it gives results. If you understand the meaning, all the better.
While Gita's emphasis is on knowledge, Sahasranama relies on the power of sound to transform. Chanting transforms. Chanting is like charging a magnet. You keep hitting a piece of iron with a magnetic field. After some time, the piece of iron becomes a magnet. Similarly, you keep chanting a mantra or take the Lord's name repeatedly, and the divine content in the mantra or the name starts getting assimilated in you, absorbing in you, and you slowly convert yourself into divinity. You start getting the qualities of the divinity whose name you are taking or whose mantra you are chanting. Your nature itself starts changing.
Why do blessings work? Blessings from a divine person.
Because through sadhana, he has more divinity in him. He is more than an ordinary man. He has more divinity in him than an ordinary man. So, when he blesses, it is as if divinity has blessed you. It comes out of sadhana, chanting, and other similar practices.
If an upasaka of Lakshmi blesses you, it is like Lakshmi is blessing you, making you richer.
If an upasaka of Ganesha blesses you, it is like Ganesha has blessed you, removing your obstacles.
If an Acharya of Vedanta blesses you, you are blessed with knowledge because that is what he has. You can only give something that you have.
The sadhaka evolves to a state when he becomes:
**अहं हरिः सर्वमिदं जनार्दनो नान्यत्ततः कारणकार्यजातम्।
ईदृङ्मनो यस्य न तस्य भूयो भवोद्भवा द्वन्द्वगदा भवन्ति॥**
All this is Janardana. There is nothing else, and I am him, Shri Hari. One who realizes this, then there are no more rebirths for him.
Why a thousand names?
One name cannot describe all the multitude of aspects of Sri Hari.
How does a civil engineer understand what he has to construct? He looks at the drawings. There is a floor plan, an elevation drawing, a cross-section drawing, and projections—like isometric or axonometric views. They all look different, but they all talk about the same object, the building to be constructed.
One view, like a photo, is not sufficient. To understand a building, he needs at least so many views. And a layman is not going to make out anything from those drawings. The engineer understands because he already has considerable understanding and knowledge about the subject. Even then, he needs five or six different views to understand what he is going to construct.
To understand divinity, five or six names are not sufficient; you need 1,000 names, at least. At least 1,000 names. Can 1,000 names describe him in full?
No.
But at least it is a starting point. Once you are in the process, you are pulled into it. Once you are tuned to the divinity with these 1,000 names, it is like just upgrading to a bigger plan with more features. It is easier. The first-time registration is more difficult.
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