According to Michael Knox Berran
Lincoln was a model writer of English prose—but he was also something else: a model of how a decent man comes to terms with the darker aspects of his own character. In Lincoln’s confession of his fascination with Macbeth he has left us a clue which, when taken together with certain passages from his speeches, and certain asides to his friends, amounts to the most elaborate and fascinating kind of confession. Those clues allow us to reconstruct, however imperfectly, the inner drama of a soul perplexed by its own ambitious yearnings—and permit us to glimpse the moral imagination of a civilized man in action.
Also interesting is Harry Jaffa’s lecture on MacBeth in which he argues
Macbeth is a moral play par excellence. In this, it stands in stark contrast to two more recent well-known tales of murder, Dostoevsky’s Crime and Punishment and Camus’s The Stranger. In Macbeth Shakespeare presented the moral phenomena in such a way that those who respond to his art must, in some way or another, become better human beings. In Dostoevsky’s and Camus’s heroic criminals we see the corruption of moral consciousness characteristic of modern literature.
See also “That old poisoner Wagner, and why art matters“.