Nirguna Brahman
Nirguna Brahman (Devanagari निर्गुण ब्रह्म, nirguṇa brahman), signifies the supreme reality without form or qualities (guna) in Hindu philosophy. The Advaita school is considered without material form. In Advaita Vedanta, the Nirguna Brahman coincides with the concept of the supreme personality known as God, or the qualities humans attribute to the deity. Nirguna Brahman is Para Brahman who is the Svayam Bhagavan.
Relationship with MulaBrahman
At the highest level, lord Siva is Sadasiva, Parameswara, or Paramasiva. In his formless (nirguna) aspect, he is the transcendental formless reality, the highest and the most unknown, who is Brahman Himself without qualities and attributes, the supreme lord, the eternal truth, the absolute, infinite, timeless, indivisible, entirely subjective Truth, which is beyond the senses and mind, without time. He is the end of all spiritual practice, the experience of pure consciousness and bliss in the state of samadhi or union. by experiencing which everything is known and realized. He is the eternal mystery mentioned in the Kena Upanishad , whom Uma Haimavathi refers as the "Spirit Supreme", by knowing whom Indra excelled all other devas and became the ruler of the heavens. According to Siva purana even Brahma and Vishnu attained the level of Trinity because of their past devotion to Nirguna Siva.[1]