It is an expression of Dostoyevsky's Christian faith. He was distraught at what he believed Catholicism was doing to his Russian Orthodox faith (that is shove it aside for atheism). A fight against atheism and for love could drive one mad, but in the end, it was only beauty that would save the world. To him that beauty and truth was found in Christ's sacrifice.

By the way, the book where the expression is written is The Idiot.