The Svetasvatara Upanishad describes Rudra, a popular epithet for Siva, as the very Brahman. According to this Upanishad the Highest Reality is verily Rudra who is without  a second.  In one of the verses we come across this firm declaration of truth, "Eko hi rudro na dvitiya tasthur." It means, Rudra is truly one and there is no place for a second. A concept that subsequently became the premise for the Non-dualistic (Advaita) school of thought.

According to the Upanishad, Siva rules (isata) these worlds with His enormous powers (isanibhi). He stands apart from all creatures (pratyan janan) and He is  the protector of all the worlds (visvabhuvana gopa). At the end of creation He withdraws these worlds into Himself. (3.2). 

He is the source and origin of all gods, the ruler of them and as Iswara gives birth to Hiranyagarbha, the golden germ. (3.4).  

White in color (aditya varnam), beyond darkness and ignorance (tamasa parastat), He alone can take us beyond the cycle of births and deaths. There  is no other path that can help us. (3.8). 

There is nothing else that is higher or smaller than Him.  He alone pervades the whole universe. (3.9). "Sa bhagavan tasmat sarva-gatas sivah." He is the Lord and He, Siva, is therefore found everywhere. (3.11).  

The Purusha of the Samkhya school is identified in this Upanishad as none other than Siva. As Purusha He controls  maya which is but Prakriti (Mayam tu prakriti viddhi, mayinam tu maheswaram). 

The Svetasvatara Upanishad reflects the sentiments and the spirit of the age in which it was composed. Saivism must have already been a popular cult in many parts of ancient India and this fact was amply established by the composer of the Upanishad through his personal spiritual experience.