Hua-yen is difficult to summarize (from Fa-tsang’s Brief Commentary, by Francis H. Cook, in Mahayana Buddhist Meditation, edited by Minoru Kiyota, 1978, Delhi 1991)

Hua-yen totalism is difficult to summarize briefly. The concrete world “out there” is a perfect fusion of the phenomenal shih and absolute li, of form se and emptiness k’ung. To say that something is empty is to say that it lacks any kind of self-existence (svabhava), and while the external world appears to be divided into many separate entities, each with a distinct form and function, all are alike empty of any substance or essence which would make them truly distinct and independent. Thus, to speak of the static relationship between things, things can be said to be essentially identical, i.e. empty of self-existence. However, this emptiness is never found apart from concrete reality, apart from “form”, to use the sutra terminology; emptiness is expressed in forms, and these forms are seen as exerting causal influences on each other. Thus to speak of their dynamic relationship, things can be said to be interdependent. Now, while it may seem strange to speak of a cosmos in which all things are identical and interdependent, these two relationships are nothing but other ways of saying that everything is empty, sarvam shunyam.

The result of this sort of analysis of the mode of being of the dharmadhatu is a de-emphasis of the differences between things and an emphasis on seeing being in its totality. Distinctions are submerged, hierarchies disappear, past, present, and future merge, and in this vast organism of interdependent parts, any part acts simultaneously as cause and effect. There is, then, a very intimate relationship between any one individual and all other individuals (or the totality). Because each and all other individuals are lacking in self-existence and have their being purely through intercausality, the whole is dependent on the part, because without the part, there can be no whole. (It must be remembered that each part has this relationship to the whole simultaneously.) At the same time, however, the part has not existence and no meaning outside the context of the totality, because is is a part of the whole. Thus, the part creates the whole and the whole creates the part, in a view of existence which Hua-yen calls fa-chieh yuan-ch’i or the interdependent origination of the cosmos (in Sanskrit dharmadhatu pratityasamutpada). Along with this interdependence, there is a relationship of essential identity among the parts of the whole.

The final consequence of this view of being is a doctrine of the completely free interfusion, or interpenetration, of the parts in the whole, and this is the distinctively Hua-yen doctrine of shih shih wu-ai, the non-impediment of a thing with any other thing. For instance, though the present is the present, because of the principle of interdependence (emptiness), the present includes past and future, which remain past and future. Or, to give another example, the practices of the boddhisattva can rightly be seen as the cause of Buddhahood-effect, but because of emptiness, they can be seen as result, because they too, in their emptiness, are merely manifestations of the Buddha [the whole]. If, as Hua-yen claims, the dharmadhatu is the body of Vairocana, where can I not find the Buddha? Everything, in fact, in the Hua-yen cosmos is worthy of respect and honor, because everything manifests the totality of being and reality.