The Kreutzer Sonata is a novella by Tolstoy. The book is about a jealous husband who overwhelmed by passions kills his wife. The book is told from the perspective of that husband who also describes to a stranger on a railway carriage his theory of where the sexual passions should place in a happy and godly life, which is not at all. The afterword makes clear that the husbands views on the train are Tolstoy's own.
I personally am not attracted to either the philosophy behind Tolstoy's views or his radical and wholesale rejection of human sexuality. Tolstoy puts this rejection in strong and inflammatory terms, but to be fair to him his doctrine is basically the same as historical Catholicism. Tolstoy sees the ideal life as sexless, because he sees sexual passions as necessarily interfering with the human striving for an ideal life. The husbands story where after a debauched youth and early adulthood he enters into a loveless marriage and then murders his wife is meant to illustrate this.
I'm not at all attracted to Tolstoy's philosophy for either theoretical or practical reasons, and I find it a little crazy to tell the truth. On the other hand, Tolstoy is both a fine writer and an acute observer of the human condition, so there is a lot of literary merit here. I think perhaps the most interesting way to read it is with the author in mind. To see it as the advocation of a monk like existence by a man with a wife and children and that the ending which is an unanswered call for forgiveness echoes Tolstoy's own feelings.