One may question that "Why? The Supreme Lord is all-good. Why He has got higher nature and lower nature?" Yes, He has got because He says. You cannot say that there is no higher nature and lower nature. There is also higher nature. Now, here the Lord says that "When I come as incarnation, when I appear..." Prakṛtiṁ svām adhiṣṭhāya. Svām means His higher nature. He does not accept this material nature. He does not accept this material nature.
Just like the example... We can give very tangible example. Just like in the prison house sometimes the head of the country goes to visit, to see, to inspect how the prison life is going on or to give them some instruction, some good lesson, that "Why you are rotting in prison? You become good citizen." Now, suppose the head of the state goes to the prison and to instruct the prisoners, and if the prisoners think, "Oh, he is also a prisoner. The head of the state who has come to instruct, he is also one of the prisoners, like us."
So similarly, if we think that Kṛṣṇa is like us, He is also assumed a material body and He is one of us, then it is a mistake. It is a mistake.