Why?

“The question of the origin of pain plays an important role in this work. In this sense, the entire development of the work leads to the drama of intervallic relationships, especially the incompatibility between the intervals of the major second and the minor second. This work is essentially a drama arising from this incompatibility. These two "intervallic persons" result from the sound of a vibrating unison. Both influence the entire sonic development of the work and both participate in the "convergence" of the sound masses in unison - that fundamental condition of the material world which combines beginning and end.
This work features a variation form. It is not about variations on a theme in this case, however, but variations on certain events: the formulation of a question or the drama of its return, or the complete modification of the sonic situation out of which such questions arise. And finally, the development of these events leads to the maximum tension of the sonic situation. In the end, this tension reveals itself as the reverse side of the maximum stasis - the vibrating unison with which the work began.”
(Sofia Gubaidulina)