1. Srimad-Bhagavatam Canto 1 - Chapter 12 - Text 16-17

2. Text 16 Daivenāpratighātena śukle saṁsthām upeyuṣi
rāto vo ’nugrahārthāya viṣṇunā prabhaviṣṇunā
The brāhmaṇas said: This spotless son has been restored by the all-powerful and all-pervasive Lord Viṣṇu, the Personality of Godhead, in order to oblige you. He was saved when he was doomed to be destroyed by an irresistible supernatural weapon.

3. Devotees protected by Lord
The child Parīkṣit was saved by Lord Kṛṣṇa for two reasons:
Mahārāja Parīkṣit - was spotless due to his being a pure devotee of the Lord
He was the only surviving male descendant of Puru, the pious forefather of the virtuous King Yudhiṣṭhira.
The 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.

4. Text 17 tasmān nāmnā viṣṇu-rāta iti loke bhaviṣyati
na sandeho mahā-bhāga mahā-bhāgavato mahān
For this reason this child will be well known in the world as one who is protected by the Personality of Godhead. O most fortunate one, there is no doubt that this child will become a first-class devotee and will be qualified with all good qualities.

5. Three grades of devotees...
Protection given by different potencies of Lord to different grades of living beings.
But Lord’s unalloyed devotees are personally protected by the Lord.
Three grades of devotees:
Kaniṣṭha-adhikārī - offer worship & respects to the Deity but without sufficient knowledge in the theological science and therefore without any respect for the devotees of the Lord.
Madhyama-adhikārī - have developed a mentality of genuine service to the Lord and who thus make friendships only with similar devotees, show favor to the neophytes and avoid the atheists.
Mahā-bhāgavata - those who see everything in the Lord and also see in everything an eternal relation of the Lord, so that there is nothing within their purview of sight except the Lord.