Adrienne Rich's poem "At a Bach Concert" deals with the fact that art and life exist with each other reciprocally. In order for art to exist, one must recognize its importance in life. Reciprocally, in order for life to "exist," one must recognize the importance of art.

For Rich, art is a "form" not unlike all other things in the world. Therefore, art has a sense of order to which it must adhere to. That being said, each artist is to determine what order they are to use as a medium in their art.

The reference to Bach is made given that Bach followed a certain order which allowed him to create the brilliant works which he created. In order to create this art, Bach needed to recognize the importance of life in art and art in life. Without this understanding, and the alignment to a form (or order), Bach's art would not have been considered something which was

too-compassionate art is half an art.
Only such proud restraining purity
Restores the else-betrayed, too-human heart.

Therefore, the main idea of Rich's poem was to show the importance of examining order, life, and art as dependant upon each other.