Brahman as the Cause
Brahman is both the material and efficient cause of the universe.
The universe emerges from Brahman like waves from the ocean. Brahman is both the substance (material cause) and the intelligence (efficient cause) of creation.
From which these beings are born, by which they live, into which they enter at death - seek to know that. That is Brahman.
This defines Brahman through its relationship to the universe.
Taittiriya Upanishad