Brahman is the material as well as the operative cause of the world for
that reason also that certain texts call it the womb, 'the maker, the
Lord, the Person, Brahman, the womb' (Mu. Up. III, 1, 3); 'that which
the wise regard as the womb of all beings' (I, 1, 6). And that 'womb'
means as much as material cause, appears from the complementary passage
'As a spider sends forth and draws in its threads' (I, 1, 7)--