Purport

As a destructive form of Shri Krishna starts unveiling, Arjuna caught himself in a strange situation, extremely scared, perplexed and confused. He has seen Lord Krishna all his life as his friend, as a happy and gentle being. Even when asking to see the original form of Shri Krishna, perhaps Arjuna has assumed of all nice things. But the fact of the matter is this universe does not only has the creation, but also destruction. In fact, construction and destruction exist in a cycle. One leads to others.

Though every human being sees these two phenomena of construction and destruction, but in small quantity and hence goes unnoticed.

But here Arjuna sees the process of destruction happening in the entire universe all at one place that too in fast forward manner. This was so much for Arjuna to comprehend. He got extremely scared, lost his peace of mind and now he asks for mercy from Bhagwan Shri Krishna.