Prabhupāda: The fighting here takes place because everyone wants to lord it over the material nature. So there is difference of interest. I want to be lord, you want to be lord: now there must be fight. But in the Vaikuṇṭha world there is one Lord and all others servitors. Therefore there is peace. So fighting was not possible in the Vaikuṇṭha world; therefore these two doorkeepers were sent to the material world by the plan of the Supreme Lord so that they could fight as Hiraṇyakaśipu and Hiraṇyākṣa with the Lord.