The child Parīkṣit was saved by the all-powerful and all-pervasive Viṣṇu (Lord Kṛṣṇa) for two reasons. The first reason is that the child in the womb of his mother was spotless due to his being a pure devotee of the Lord. The second reason is that the child was the only surviving male descendant of Puru, the pious forefather of the virtuous King Yudhiṣṭhira. The Lord wants to continue the line of pious kings to rule over the earth as His representatives for the actual progress of a peaceful and prosperous life. After the Battle of Kurukṣetra, even up to the next generation of Mahārāja Yudhiṣṭhira was annihilated, and there were none who could generate another son in the great royal family. Mahārāja Parīkṣit, the son of Abhimanyu, was the only surviving heir apparent in the family, and by the irresistible supernatural brahmāstra weapon of Aśvatthāmā, he was forced to be annihilated. Lord Kṛṣṇa is described herein as Viṣṇu, and this is also significant. Lord Kṛṣṇa, the original Personality of Godhead, does the work of protection and annihilation in His capacity of Viṣṇu. Lord Viṣṇu is the plenary expansion of Lord Kṛṣṇa. The all-pervasive activities of the Lord are executed by Him in His Viṣṇu feature. Child Parīkṣit is described here as spotlessly white because he is an unalloyed devotee of the Lord. Such unalloyed devotees of the Lord appear on the earth just to execute the mission of the Lord. The Lord desires the conditioned souls hovering in the material creation to be reclaimed to go back home, back to Godhead, and thus He helps them by preparing the transcendental literatures like the Vedas, by sending missionaries of saints and sages and by deputing His representative, the spiritual master. Such transcendental literatures, missionaries and representatives of the Lord are spotlessly white because the contamination of the material qualities cannot even touch them. They are always protected by the Lord when they are threatened with annihilation. Such foolish threats are made by the gross materialists. The brahmāstra, which was thrown by Aśvatthāmā at the child Parīkṣit, was certainly supernaturally powerful, and nothing of the material world could resist its force of penetration. But the all-powerful Lord, who is present everywhere, within and without, could counteract it by His all-powerful potency just to save a bona fide servant of the Lord and descendant of another devotee, Mahārāja Yudhiṣṭhira, who was always obliged by the Lord by His causeless mercy.