The word "Upanishad" means the knowledge a Guru, well versed in the Vedas, imparts to his disciple, seated near him. The Vedas provide two kinds of knowledge - para and apara. Apara vidya consists of knowledge which leads to material prosperity, but para vidya leads one to mokshaor liberation. Para vidya consists of the right knowledge of God and means of reaching Him. Para vidya is superior to apara vidya. This para vidya of the Vedas is contained in the heart of the Vedas, the Upanishads.
The Upanishads are also known as Vedanta or the conclusions of the Vedas. Bhakti is the only means of achieving moksha in this age, the Kali
हरिः ॐ | द्वापरान्ते नारदो ब्रह्मानं जगाम कथं भगवान गम
पर्यतन कलीम संतारेयम इति |
At the end of Dvapara Yuga, Narada, after traveling the world,
approached Lord Brahma and asked him: 'How may I overcome the (evil
effects of) the Kali Yuga?
सा होवासा ब्रह्मा साधू प्रष्टो अस्मि
सर्वस्रुतिराहस्यम गोप्यं ताच्च्रउनु येनः कलिसम्सरम तरिश्यसी |
Brahma said: You have asked me an excellent question. I shall reveal
to you the secret of all Vedas, by which you will cross over the
(ocean of) samsara filled with the bad effects of the Kali Yuga. This
secret must be preserved and protected.
भगवतः अदिपुरुशास्य नारायणस्य नामोच्कारानामात्रेना निर्ध्र्ताकलिर
भवति| नारदः पुनः पप्रच्चा तन्नामा किमिति |
By merely uttering the names of the Primeval Purusha, who is
Bhagavan Narayana, one is freed from the clutches of Kali. Narada
asked again: What are those names of Narayana?
सा होवासा हिरान्यगार्भः |
हरे रामा हरे रामा रामा रामा हरे हरे |
हरे कृष्णा हरे कृष्णा कृष्णा कृष्णा हरे हरे |
इति शोडासका नमनाम कलिकल्माशानासनाम |
नतः परतारोपयाह सर्ववेदेषु द्र्स्यते |
Lord Brahma said: 'O Hari, O Rama, O Hari, O Rama, O Rama O Rama, O
Hari, O Hari! O Hari, O Krishna, O Hari, O Krishna, O Krishna O
Krishna, O Hari, O Hari! This collection of sixteen names (of
Narayana) destroys the evils of the Kali Yuga. I don't see any other
effective means (of liberation) in the Vedas.
इति शोदासकलाव्र्तस्य जिवास्यावारानाविनासनाम |
ततः प्रकासते परम ब्रह्मा मेघपये रविरास्मिमंदालिवेती |
(This mantra) destroys the sixteen kalas of the jiva, beginning with
the prana, which constitute the veil of ignorance. Then the Supreme
Brahman shines forth, just as the solar disc shines forth brilliantly
when the clouds vanish.
पुनार्नारादाह पप्रच्चा भगवान को अस्य विधिरिति |
तम होवासा नास्य विधिरिति |
Narada asked: O Bhagavan, what are the regulations or injunctions to
be followed in chanting these names? Brahma said: There are no
regulations to be followed.
सर्वदा सुसिरासुसिर्वा पठान ब्रह्मणः सलोकताम समीपतम सर
उपतं सयुज्यतामेती |
By chanting these names always, whether in a clean or unclean state,
a brahmana obtains the four kinds of liberation, sAlokya, sAmIpya,
यदस्य शोदासिकस्य सर्धत्रिकोतिर्जपति तदा ब्रह्महत्यम
तरति तरति विराहत्यम |
When a brahmana chants this mantra of sixteen names, for a total of
one and one half crore times, he becomes free from the sin of killing
a brahmaNa. He overcomes the sin of neglecting his domestic fire.
स्वर्नास्तेयत पूतो भवति |
पित्र्देवामानुश्यनामापकारत पूतो भवति |
He becomes free from the sin of stealing gold. He becomes free from
the offenses committed against forefathers, Gods and human beings.
सर्वाधार्मापरित्यागापपट सदा सुसितामाप्नुयत |
सद्यो मुच्यते सद्यो मुच्यते इत्युपनिषत |
He quickly becomes free from the sin of giving up all religious
duties. He becomes liberated immediately; he becomes liberated
immediately. Thus the Upanishad.