The universal form that Arjun beholds is just another aspect of Shree Krishna’s personality and is non-different from him. And yet, the vision of it has dried up the camaraderie that Arjun was previously experiencing toward Shree Krishna, and he is overcome with fear. Seeing the many wondrous and amazingly frightful manifestations of the Lord, Arjun is now scared, and thinks that Shree Krishna is angry with him. So he asks for mercy.