"Pale are the words I build for my delight"

Pale are the words I build for my delight
To house in; pale as the chill mist that holds
An ardent morn. My fire to others' sight
But dimly burns through the frail speech it moulds;
I cast but shadows from my inward light.
But, O my Joy, thou understandest well
Both what I can and what I cannot tell.