There is a vitality, a life force, a quickening
that is translated through you into action,
and because there is only one of you in all time,
this expression is unique.

If you block it,
it will never exist through any other medium
and be lost.
The world will not have it.

It is not yours to determine how good it is;
nor how it compares with other expressions.
It is your business to keep the channel open.
You do not even have to believe in yourself or your work.
You have to keep open and aware directly
to the urges that motivate you.

Keep the channel open.
No artist is ever pleased.
There is no satisfaction whatever at any time.
There is only a queer divine dissatisfaction;
a blessed unrest that keeps us marching
and makes us more alive than the others.

— Martha Graham to Agnes De Mille

I think it's more advice or instruction than philosophy. It doesn't attempt to answer any questions or explain any mysteries.

Advice can be based on a philosophy, as is hinted at in the first sentence, but a significant explanation is missing.