What is the power of the Narayana Kavacha mantram that appears in the Bhagavatham?
What is the meaning of this mantram and how do you get the benefits of the mantra?
The Narayana Kavacha is described in this chapter of the Srimad Bhagavatam. As I discuss in this question, Trisiras (AKA Vishwarupa) was the three-headed son of the divine architect Tvashta (AKA Vishwakarma), and he was killed by Indra. But before all that, Trisiras temporarily served as guru of the gods when Brihaspati had abandoned them out of anger. During this time, Indra asked Trisiras how he could equip himself with the Narayana Kavacha (armor of Vishnu) so that he could defeat the Asuras. Here is the procedure that Trisiras told Indra:
One puts on armor in case one is overcome by fear. [For His purpose arming oneself] one should first wash one's hands and feet and then after saying the required mantra [doing âcamana, three times over] sip water. Sitting down, facing the north one next should ritually purify oneself [in pavrita 'touching kus'a'] by preparing oneself mentally in silence. Thus in dedication to the lordship of Nârâyana being innerly cleansed one should adopt the defense in which one, beginning with saying 'om', offers one's obeisances to Nârâyana by designating two mantras to one's body [by nyâsa], that is to say the [eight syllables of the] mantra 'om namo nârâyanâya' to each of the [eight] parts of the body, touching therewith [consecutively] one's lower legs, knees, thighs, abdomen, heart, chest, mouth and [top of the] head, or even repeat this in reverse order [beginning with ya, which is called respectively utpatti-nyâsa and samhâra-nyâsa].
Next one should assign the [twelve] syllables of the mantra beginning with om and ending with ya [om namo bhagavate vâsudevâya] to the [twelve parts of the] fingers starting with the [tip of the] index finger and ending with the four joints of the two thumbs. [Then chanting the mantra 'om vishnave namah', All glories to Lord Vishnu] the heart should be assigned 'om', 'vi' next comes to the top of the head, 'sha' comes between the eyebrows, 'na' on the s'ikhâ [the tuft of hair on the back of the head with Vaishnava monks], 've' comes between the eyes, the syllable 'na' should be assigned to all the joints of the body and 'mah' should be thought of as a weapon in the form of a mantra, so that one becomes an intelligent [representative of it]. By [finally] saying the mantra beginning with a visarga [an aspirated 'ha'] and ending with 'phath' ['mah astrâya phath' or: 'thus I call for my weapon'], one should be fixed on the respect for Lord Vishnu in every possible way. One should recite the following prayer representing the Supreme Self to meditate upon that [in the form of Bhagavân] is endowed with the six opulences of learning [or knowledge], power and austerity [as also wealth, beauty and fame].
And here is the meaning of the Narayana Kavacha mantra itself, which you're supposed to say after doing the above:
I pray that the Lord of the eight qualities [see also 3.15: 45] whose feet rest upon the back of Garuda and who holds the conch shell, disc, shield, sword, club, arrows, bow and ropes in his eight hands, will protect me on all sides. May Matsya [the fish incarnation of Lord Vishnu] protect me against the aquatic predators in the water who represent the noose of Varuna. May He as the dwarf incarnation Vâmana who took the three steps [as Trivikrama, Lord Vishnu as the conqueror of the three worlds] protect me on land and may He as Vis'varûpa [Him in the form of the universe] protect me in the sky [the ether]. May the Supreme Master Lord Nrisimhadeva whose fearful laughter resounding in all directions meant the fall of the enemy of the leader of the demons [Hiranyakas'ipu] and the miscarriage of his babies, protect me in [my toiling in] the wilderness and on the front in battle. May we in the streets be protected [against thugs] by Him whom one respects with the rituals, Lord Varâha who raised the planet earth on His tusks. May there for us on the mountain tops be the protection of Lord [Paras'u-]Râma and may we in foreign countries be protected by [Lord Râmacandra] the elder brother of Bharata and His brother Lakshmana. May Lord Nârâyana protect me against religious fanaticism and keep me from acting in madness, may Nara keep me from being arrogant, may Dattâtreya the master of [the powers of] yoga keep me from straying from the path of yoga and may Kapila, the Lord of [all good] qualities, keep me from attachment to the fruits of labor.
May Sanat-kumâra [the perfect celibate] protect me against Cupid [lust], may Hayagrîva [the horse incarnation] keep me from the path of disrespecting the divinity, may the best of all sages the devarshi Nârada keep me from offenses during the service and may the Lord in the form of Kûrma [the tortoise incarnation] keep me out of the everlasting hell. May Bhagavân Dhanvantari [the physician avatâra] protect me against things harmful to one's health, may Rishabhadeva, the one fully in control of the mind and the self, keep me from duality and fear, may Yajña [Vishnu as the Lord of sacrifice] keep me from infamy and an awkward social position and may Lord Balarâma in the form of Ananta S'esha keep me away from the angry serpents. May Bhagavân Dvaipâyana [Vyâsadeva] keep me from ignorance and may Lord Buddha protect me against the hosts of heretics and madness [as a consequence of negligence]. May Kalki, the Lord who in this darkest age of quarrel incarnates as the greatest one in defense of the dharma [also as the channa- or covert avatâra], protect me against the impurities of the time we are living in [viz. intoxication, promiscuity, gambling and meat-eating; see also 1.17: 24].
May Kes'ava protect me with His club during the hours after sunrise, may Govinda holding His flute protect me early in the morning, may Nârâyana the Lord of all potencies, protect me late in the morning and may Lord Vishnu the ruler with the disc in His hand, protect me during the hours at noon. May Lord Madhusûdana with the fearful bow S'ârnga protect me early in the afternoon. May Mâdhava, the Lord of Brahmâ, Vishnu and S'iva, protect me in the late afternoon and may Lord Hrishîkes'a protect me during the hours at dusk. May Lord Padmanâbha [the Lord from whose navel the universe sprang] be the one protector during the entire evening early and late. May the Lord with the S'rîvatsa mark protect me during the hours after midnight, may Janârdana the Lord with the sword in His hand protect me late at night and may Lord Dâmodara protect me during the hours before dawn [during which there is the brâhmamuhûrta]. May the Controller of the Universe, the Supreme Lord in the form of time protect me.
Please let the sharp rimmed [Sudars'ana] disc that wielded by the Lord destructively moves in all directions alike the fire at the end of time, burn to ashes the enemy forces, the same way a blazing fire with its friend the wind would burn dry grass in an instant. May You [Kaumodakî], oh mace so dear to the Invincible Lord, whose impact sparks with fire like thunderbolts, pound to pieces, smash, destroy and pulverize my enemies the imps [Kushmândas], the magicians [Vainâyakas], the evil spirits [Yakshas], the demons [Râkshasas], the ghosts [Bhûtas] and the maddeners [Grahas]. Oh conch shell [oh Pâñcajanya], may you with your frightening sound make the hearts tremble of the enemy torturers [Pramathas], evil spirits [Pretas], she-devils [Mâtâs], madmen [Pis'âcas] and heretics [Vipra-grahas] with their evil looks. You oh sharpest of all swords [oh Nandaka], may you in the hands of the Lord cut to pieces, chop up the enemy soldiers. Oh shield marked with a hundred shining moons, blind the eyes of the evil-minded ones so full of anger and pluck out their sinful eyeballs. May by the glory of Your name, form and attributes all the bad [influence of the] planets, falling stars, sinners, snakes, scorpions, predators and other living beings and fear arousing poisoners of our minds and bodies who obstruct our well-being, be completely destroyed. May the majesty of Garuda whom one praises in hymns, he who embodies the Vedic verses, may that master protect us with [his name and] all the names of Vishvaksena [the Lord whose powers are found throughout the universe] against an endless suffering. May His holy names, forms, strategies ['carriers'] and weapons, protect our intelligence, mind and life air from being caught in fear.
We pray that whatever that is disturbing us [and our devotion] will find its end as a logical consequence of the fact that it is You, the Lord [of time] alone who decides what the ultimate reality would be of that what is and that what is not. Those bent upon an absence of differences think of the oneness of the Soul [within the material diversity]. Following that course, He is truly understood as the [One transcendental] omniscient Supreme Lord [who defeats the illusion] by means of His expanding spiritual energy in the form of His decorations, weapons, characteristics and the opulence of His many potencies and different names. May He, the all-pervading One, with all His forms protect us always and everywhere. May the Supreme Lord in every nook and corner, in all directions, above and below, on all sides, from within and from without, in the form of Nrisimhadeva annihilate all worldly fears with His mighty roar [or song, see the Nrisimha Pranâma]. May He with His effulgence overshadow all other influences.
(Whew! That was long.). And here is how Trisiras describes the power of the Narayana Kavacha:
Whoever keeps this [prayer] in mind will, whatever he came to see, found at his feet or stumbled upon, immediately be freed from all fright and fear. He who employs this mystic prayer has nothing to fear, not from the government, not from rogues, not from maddeners and such nor from any disease at any time. This prayer was in the past used by a man called Kaus'ika, a brahmin who fixed in yoga gave up his body in the desert. His remains were spotted by Citraratha, the king of the Ghandarvas from above in his heavenly chariot, when he one day, surrounded by many a beautiful woman, had moved in the direction where the twice-born one had died. All of a sudden he with his heavenly vehicle, his vimâna, inescapably tumbled out of the sky. Amazed about it he consulted with the Vâlikhilyas [the sages of the sun god] who advised him to collect the bones, throw them in the eastward flowing Sarasvatî and then return home after taking a bath in that river.
And we can add to this the example of Indra himself, who after learning all this from Trisiras was able to defeat the Asuras in battle.
By the way, I quoted the Aadhar translation, rather than the Prabhupada translation I usually quote, because the Prabhupada translation of this passage seemed to contain a lot of inaccuracies. But of course, you need to say the actual Narayana Kavacha mantra in Sanskrit, not English, so just to get the Sanskrit text you can use this page on Prabhupads's site. Verses 12-34 make up the Narayna Kavacha mantra.