Krishna introduces the concept of Nirguna Brahman as the ultimate reality beyond the conventional theistic idea of God and religion. Advaita Vedanta emphasizes that Nirguna Brahman is a higher reality, an absolute reality without any qualifications or adjectives. It is described as pure being, existence itself, pure awareness, and pure bliss. This concept can only be approximated through negation, known as the apathetic method, where the ultimate reality is pointed out by what it is not.