The transcendental forms and pastimes of the Lord, as described in Bhagavad-gītā, are difficult subject matters for those who are not devotees to understand. The Lord never reveals Himself to persons like the jñānīs and yogīs. And there are others who, because of their envying the Lord from the bottom of their hearts, are classified amongst the beasts, and for such envious beasts the subject matter of the Lord's appearance and disappearance is simply a mental disturbance. As confirmed in Bhagavad-gītā (BG 7.15), the miscreants who are simply concerned with material enjoyment, who work very hard like beasts of burden, can hardly know the Personality of Godhead at any stage due to āsurika-bhāva, or a spirit of revolt against the Supreme Lord.
The transcendental bodily expansions manifested by the Lord for His pastimes in the mortal world, and the appearance and disappearance of such transcendental expansions, are difficult subject matters, and those who are not devotees are advised not to discuss the Lord's appearance and disappearance, lest they commit further offenses at the lotus feet of the Lord. The more they discuss the transcendental appearance and disappearance of the Lord in the asuric spirit, the more they enter into the darkest region of hell, as stated in Bhagavad-gītā (BG 16.20). Anyone who is against the transcendental loving service of the Lord is more or less a beastly creature, as confirmed in this verse of Śrīmad-Bhāgavatam.