Everything that is seen in the universe, the forms appear different only due to ignorance or thinking through the identification of the body as I. Everything that is seen is nothing but that supreme reality called Brahman alone—free of all defects. Sri Adi Sankaracharya, in the Vivekachoodamani, gives a beautiful example to illustrate this point. Every part of the pot is, in fact, essentially clay only. So what needs to be called clay in reality is being called a pot! That existence of a pot is illusory. What exists is only clay.
In the same way, all the forms are nothing but various permutations and combinations of the five elements—earth, water, fire, air, space—and their essences which express as smell from the earth, taste from water, form from fire/heat, feeling from air and sound from space. Yet when they combine in various ways to create different forms of animals, plants, insects, objects and humans—we call them by different names and get deluded as a result.
Though as a thought we may appreciate the beauty of this idea that all is that Brahman alone, the moment we rise up from the thought and interact with the world, we forget this and enter into our petty squabbles, fights and oneupmanship, forgetting that all that is, is the supreme reality alone. All that competition and strife is only our self competing with our self, imagining all the time that it is me against another person, object or situation.
Try as one might, it cannot be disproved by anyone that the content of the mud pot is actually only mud. In the same way, how much ever we may extend our logic it is impossible that the content of this world that we see is anything other than the supreme essence—Brahman alone. Just as the nomenclature of pot for the mud is a false and temporary reality, calling the Brahman as the world is also a mere word without any truth as its basis. The Acharya puts it a little humorously that if someone says, “Yes, I do see a world out there,” then it is like the words of a blabbering somniloquist! The Atharva Veda says that this world is Brahman alone and the Acharya cites that reference. The names and forms that are superimposed are also not different from the Brahman.