According to Kant's moral philosophy, actions such as lying were not permissible because they could not be coherently "universalized". So if everyone lied all the time, it would undermine the very concept of lying, because no one would believe anything anyone said, making lying pointless. In addition, Kant believe that for an action to be moral, it had to be done out of a sense of duty. If you save someone from a burning building because you want a reward, or because you will be punished if you don't do it, you aren't doing anything moral - you must do it out of your moral duty to save them.