Why did Lord Vishnu have to incarnate as Narasimha?

Shri Manikanta asked: God Narasiṃha is God Viṣṇu, who is the ultimate power. Could He not have directly come and killed the demon Hiraṇyakaśipu? What was the necessity for Him to come as Narasiṃha, a human being with the head of a lion?

Swami replied: A rowdy misuses his power and gains victory over his opponents by violating established rules. A good administrator, who is very intelligent, succeeds even without violating any rule. He is also able to interpret the rules properly and prove that his victory was justified. The demon Hiraṇyakaśipu had got a boon from God Brahmā. There is no difference between God Brahmā and God Viṣṇu (Brahmāca Nārāyaṇaḥ—Veda). This means God Viṣṇu Himself gave the boon to the demon in the form of God Brahmā, as a reward for the demon’s severe penance. God Viṣṇu could have come directly and killed the demon using His power, violating the boon given by Himself. But, in that case, God Viṣṇu would have appeared to be like a rowdy misusing His brutal power. But God Viṣṇu is the most intelligent administrator of creation and He could easily kill the demon, meeting all the conditions of His own boon given to the demon.

The demon had desired for immortality, which was denied. Instead, he was told by God Brahmā to specify the conditions under which he could not be killed and that boon would be granted. So, the demon had asked that no species within creation should be able to kill him. Narasiṃha was neither a human being nor a lion. The other condition specified by the demon was that he should not be killed inside the house or outside the house. Narasiṃha killed the demon on the doorstep, which was neither inside the house nor outside the house . The demon had asked that he should neither be killed during the day nor during the night. God killed him at twilight, as the sun was setting, which is neither day nor night. In this manner, God did not violate any condition of the boon and yet, killed the demon. This shows the supreme intelligence of God, as said in the Veda (Sa sarvajñaḥ sarvavit). God is not only the most powerful but also the most intelligent.