In Shrimad Bhagvad Gita, it is stated that avyaya is the cause of this whole universe. This can be understood by learning that there are two types of causes. One is that which results in an ``effect``.
The second produces no effect. Ávyaya falls in the second category; it can reveal the existence of whole universe by its sheer presence. Take for example, eyes; they can see an object, it is the effect.
The sun or a lamp, on the other hand, does not see an object. The light from the sun or lamp help me see the object. But the sun or lamp in themselves are not the cause of the object. They do not perform any specific action in sighting the object. Even without any specific action, they cause the object to be seen.
Avyaya has five components—ananda, vijnana,mana, prana and vak.
A more detailed and lucid explanation of avyavya can be found in The Cosmic Matrix—in the light of the Vedas, authored by Rishi Kumar Mishra. Publisher: Rupa & co.