To strengthen the teaching of “Dharma-Dharmatama-Vibhaga”, Krishna shows His vast form to Arjun. This Vast form of Krishna is graphical representation of “Cosmic Impermanence”. In the vast form of Krishna, everything is fluid. All the living beings are constantly dying and constantly taking rebirths. The planets continue to crash amongst each other and continue to form again. The scene cannot be imagined, as it is unimaginably dynamic.
Miteiya in his book describes this event to explain Impermanence. With Impermanence, the division between Dharma and Dharmatama extinguishes. There is no boundary between a Doer and the actions.