It is similar to the stories of Zen, about the teachings being a boat to take you to the other side of the river. Once you reach the other shore, you shed the boat.
The poem hints at the true reality experience, but it cannot provide it, no words can.
My interpretation:
The foundation of thought and language is categories and pattern matching; every word/thought is meaningful only in that it includes some parts of reality and excludes other. Thus, the true unity of reality can never be named, only experienced if you are really, really quiet.
A thing, like the late Alan Watts so eloquently put it, is really a think - a unit of thought. Words are phonetic reflections of thoughts and they are the mother of all things.
But all of reality is a unity, everything springs from the same source. But even so, all the different things, and the experience of them, are all within that said unity.
Fun experiment: Putting it in different clothes (and please don't put too much of your pre-conceived notions of what the words mean into it, use it instead to try to see these old words in a new light).
The name of God can never be mentioned,
and none of the named gods are real.
God is the creator of Heaven and Earth,
The devil is the father of 10000 lies.
In virtue, you can approach God.
In sin, there is only the Devil.
The Will of God is mysterious
but both virtue and sin lie within it
Look within
and all shall be revealed.