Pure devotion to duty is a momentary victory of freedom over determinism. The more a human acts freely, the more he does what he does simply because he ought to, the more he comes to believe that he is free, a free agent, independent of the dependency-chain of external matter in motion. He believes, he assumes, that he is free. And the more he acts morally and does not simply look back at what he has done empirically, the more his conviction is intensified. Knowledge before the fact and knowledge after the fact is not action, but interpretation of action.
Interpretation always explains action as the result of certain causes and conditions.
Moral action, however, is, at the moment of acting, when one does not self-consciously look backwards or forwards, a timeless moment of freedom, a moment of pure undetermined and spontaneous willing. Thus, a human being can not know himself as he really is, but he can be himself most completely when he acts freely and morally. Freedom cannot be observed, but it can be exercised. The absolute moral law determined by practical reason is a categorical not a hypothetical imperative. If I want to go to heaven, I must act morally.