The main image of Dharmadhatu is that of space - the 'space of all things' within which all phenomena manifest,
abide and dissolve back into. This is similar to physical space,
which is like a container within which the remaining four elements appear,
abide and disappear. These four elements do not come out of any
other source; they emerge from space itselt. They do not remain anywhere
else other than within space; neither do they go anywhere outside
of space.
In the same way, dharmadhatu is the basic environment
of all phenomena, whether they belong to samsara or nirvana. It encompasses
whatever appears and exists, including the worlds and all
beings. Everything takes place within and dissolves back into the state
of dharmadhatu. Dharmadhatu encompasses all of samsara and nirvana
-it doesn't include only nirvana and exclude samsara; it's not like that,
External phenomena appear within space, remain within space and
disappear within space again.
As it is / Rangjung Yeshe Publications