"Duty has the virtue of making us feel the reality of a positive world while at the same time detaching us from it." (From Journal Intime)
This is a penetrating observation, and a perfect specimen of the aphorist's art. It is terse, true, but not trite. The tip of an iceberg of thought, it invites exploration below the water line.
If the world were literally a dream, there would be no need to act in it or take it seriously. One could treat it as one who dreams lucidly can treat a dream: one lies back and enjoys the show in the knowledge that it is only a dream. But to the extent that I feel duty-bound to do this or refrain from that, I take the world to be real, to be more than maya or illusion. Feeling duty-bound, I help realize the world. It is an "unfinished universe" in a Jamesian phrase and I cannot play within it the role of mere spectator. I must play the agent as well; I must participate whether I like it or not, non-participation being but a deficient mode of participation. In a Sartrean phrase, I am "condemned to be free": I am free to do and leave undone, but my being free does not fall within the ambit of my freedom.
And to the extent that I feel duty-bound to do something, to make real what merely ought to be, I am referred to this positive world as to the locus of realization.
But just how real is the world of our ordinary waking experience? Is it the ne plus ultra of reality? Its manifest deficiency gives the lie to this supposition, which is why great philosophers from Plato to Bradley have denied ultimate reality to the sense world. Things are not the way they ought to be, and things are the way they ought not be, and everyone with moral sense feels this to be true. The Real falls short of the Ideal, and, falling short demonstrates its lack of plenary reality. So while the perception of duty realizes the world, it also and by the same stroke de-realizes it by measuring it against a standard from elsewhere.
The moral sense discloses a world poised between the unreality of the dream and the plenary reality of the Absolute. Plato had it right: the human condition is speleological and the true philosopher is a transcendental speleologist.
The sense of duty detaches us from the world of what is by referring us to what ought to be. What ought to be, however, in many cases is not; hence we are referred back to the world of what is as the scene wherein alone ideals can be realized.
It is a curious dialectic. The Real falls short of the Ideal and is what is is in virtue of this falling short. The Ideal, however, is only imperfectly realized here below. Much of the ideal lacks reality just as much of the Real lacks ideality. Each is what it is by not being what it is not. And we moral agents are caught in this interplay. We are citizens of two worlds and must play the ambassador between them.