Early in Dostoevsky's novel The Brothers Karamazov, a wealthy woman asks Staretz Zosima how she can really know that God exists. The elderly monk tells her that no explanation or argument can achieve this, only the practice of "active love."
The woman then confesses that sometimes she dreams about a life of loving service to others - she thinks perhaps she will become a Sister of Mercy, live in holy poverty, and serve the poor in the humblest way. But then it crosses her mind how ungrateful some of the people she would serve are likely to be. They would probably complain that the soup she served wasn't hot enough or that the bread wasn't fresh enough or the bed was too hard. She confesses that she couldn't bear such ingratitude - and so her dreams about serving others vanish, and once again she finds herself wondering if there really is a God. To this the Staretz responds, "Love in practice is a harsh and dreadful thing compared to love in dreams."
I often heard Dorothy Day recite those words. I doubt any chapter in any work of literature had so much importance for her. She had first read Dostoevsky's novel when she was in her teens. It was partly through Dostoevsky that she formed an understanding of Christianity that wasn't typically Western, seeing it not simply as an institutional structure but as a way of life in which nothing was more important than seeing Christ in others.