What is the theme in The Grand Inquisitor by Fyodor Dostoevsky?

Throughout his life Dostoevsky used his writing to explore the issue of free will. He believed that human beings are given free will, and that they must constantly choose between good and evil. It is not an easy choice, and God and the devil battle each other for the possession of every soul. Dostoevsky was conscious of this struggle all his life. He wished to believe, yet his intellect kept raising doubts. For him, the question of free will was central to his understanding of humans and society.