Prahlāda Mahārāja's demoniac father had repeatedly threatened to kill Prahlāda, but Prahlāda was confident that he could not be killed, since he was protected by the Supreme Lord. By appearing from the pillar, the Lord encouraged His devotee, saying in effect, "Don't worry. I am present here." By manifesting His form as Nṛsiṁhadeva, the Lord also preserved the truth of Lord Brahmā's promise that Hiraṇyakaśipu was not to be killed by any animal or any man. The Lord appeared in a form that could not be said to be fully a man or a lion.
Śrīmad-Bhāgavatam 7.8.17, Purport (Excerpt)
