When in deep sleep, we don’t recognize the universe - we know nothing. The Purushasukta says that the universe and the individual need to ‘interact’ for the universe to be validated. Else, the universe does NOT exist for us. This connection is presented symbolically in the sacrificial fire analogy as a ‘pouring in’ of the 21 elements we are built up with INTO the supreme sacrifice / yagna/ sacrificial fire that is built by the seven elements - 5 basic elements, cosmic mind and cosmic ego.