Non-Buddhists conceive of the Universe as things within space. And in the space between things there is room for judgement, room for manipulation.
For Dogen, the realm of nonduality is the realm of intimacy. It is not that there is no differentiation, but there is no gap, no void.
And within that intimacy, each dharma totally occupies its own space. One dharma does not obstruct another, just as one moment does not obstruct another. The total exertion of one dharma–the exemplar of exertion being zazen–is the total exertion of all dharmas, because there is no separation.
The total exertion of one dharma makes real the whole Universe.