In sex life, the combination of matter from the parents, which involves emulsification and secretion, creates the situation whereby a soul is received within matter, and the combination of matter gradually develops into a complete body. The same principle exists in the universal creation: the ingredients were present, but only when the Lord entered into the material elements was matter actually agitated. That is the cause of creation. We can see this in our ordinary experience. Although we may have clay, water, and fire, the elements take the shape of brick only when we labor to combine them. Without the living energy, there is no possibility that matter can take shape. Similarly, this material world does not develop unless agitated by the Supreme Lord as the Virat-purusa. Yasmad udatisthad asau Virat: by His agitation, space was created, and the universal form of the Lord also manifested therein.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Third Canto, Chapter 26 – Text 51