In this appearance Lord Vishu assumed the form of half man half lion, at twilight, manifesting himself from a pillar to kill the demon Hiranyakashipu. Pralad, son of Hiranyakashipu is a very devoted soul and always absorbs his mind, words and actions in the devotional service of Lord Vishnu so much that the Lord appeared personally to give him protection from his demon father who was trying to kill him..

The Personality of Godhead assumed the form of Nrsimha dev in order to vanquish the great fears of the demigods. He killed the king of the demons [Hiranyakashipu], who challenged the Lord with a club in his hand, by placing the demon on His thighs and piercing him with His nails, rolling His eyebrows in anger and showing His fearful teeth and mouth.

The history of Prahlada Maharaja, the great devotee of , Nrsimha dev is narrated in the Seventh Canto of Srimad-Bhagavatam. Prahlada Maharaja, a small child of only five years, became the object of envy for his great father, Hiranyakashipu, only because of his becoming a pure devotee of the Lord. Demons cannot stand to hear the glories of the lord and feel that they should get praise for any great accomplishment. The demon father employed all his weapons to kill his devotee son, Prahlada, but by the grace of the Lord he was saved from all sorts of dangerous actions by his father. He was thrown in a fire, in boiling oil, from the top of a hill, underneath the legs of an elephant, and he was administered poison. At last the father himself took up a chopper to kill his son, and thus Nrsimha deva appeared and killed the heinous father in the presence of the son. Thus no one can kill the devotee of the Lord. Similarly, Arjuna was also saved by the Lord, although all dangerous weapons were employed by his great opponents like Bhisma.

Prahlada Maharaja requested Lord Nrsimha dev to deliver his sinful father, who had so many times offended the lotus feet of the Lord. The Lord replied that in a family where a Vaisnava like Prahlada is born, not only his father but his father's father and their fathers—up to the fourteenth father back—are all automatically delivered.
 

Brahmana, the topmost section of human society, are mostly devotees. They are generally unaware of the happenings within the material world because they are always busy in their activities for spiritual advancement. Nonetheless, when there is a calamity in human society, they cannot remain impartial. If they do not do something to relieve the distressed condition of human society, it is said that due to such neglect their spiritual knowledge diminishes. Almost all the sages go to the Himalayas for their personal benefit, but Prahlada Maharaja said that he did not want liberation alone. He decided to wait until he was able to deliver all the fallen souls of the world.

This is a sign of associating with great devotees. A devotee takes instructions from a liberated soul and is thus overwhelmed by ecstasy from transcendental pleasure. As stated by Prahlada Maharaja:

(SB 7.5.32)

One cannot become a perfect devotee of the Lord without having touched the lotus feet of a great devotee. One who has nothing to do with this material world is called niskinchina . The process of self realization and the path home, back to Godhead, means surrendering to the bona fide spiritual master and taking the dust of his lotus feet on one's head. Thus one advances on the path of transcendental realization. Vidura had this relationship with Maitreya, and he attained the results.

SB 4.31.29
TEXT 29

Suka Dev Goswami continued: My dear King, Lord Nrshima dev resides in the tract of land known as Hari-varsa. In the Seventh Canto of Srimand-Bhagavatam, I shall describe to you how Prahlada Maharaja caused the Lord to assume the form of Nrsimha deva. Prahlada Maharaja, the topmost devotee of the Lord, is a reservoir of all the good qualities of great personalities. His character and activities have delivered all the fallen members of his demoniac family. Lord Nrsimha dev is very dear to this exalted personality. Thus Prahlada Maharaja, along with his servants and all the denizens of Hari-varsa, worships Lord Nrsimha dev.