Philosophy
Kant derives moral obligation from autonomy, rational consistency and respect for persons rather than consequences or inclination.
An action earns moral esteem only when it is done because it is right, not because it pays off or because we feel like doing it. Two people can perform the same helpful act, yet only the one acting from duty has done something morally worthy.
What makes an act right is the rule the person chooses to act on, not the result it achieves. A dutiful act keeps its worth even if its goal is never realised, because its value lies in the principle behind the choice.
You cannot be ordered to feel affection, so a duty to love, even toward an enemy, can only mean a duty to act with goodwill, not to feel warmth. Morality governs what we choose, not what we happen to feel.
Morality grounded in reason alone is reliable and self-sufficient, whereas support from desire is fickle and may vanish when circumstances change. Acting well only because you want to leaves goodness at the mercy of moods.
Ordinary moral reasoning is prone to bending duty to suit what we want. A precisely stated moral law protects against these self-serving excuses by fixing what is required before desire starts arguing.
The supreme moral principle is a command that binds every rational being unconditionally, whatever they happen to want. It asks whether the principle behind your action could hold as a law for everyone. Kant presents this as the single foundation of moral reasoning, though critics dispute whether he grounded it securely.
Because people can reason and govern themselves, they are ends in themselves and must never be used by anyone merely as a means. This capacity for freedom lifts them above beings that are simply pushed around by nature.
Unconditional obligations are not imposed from outside but express our own capacity to govern ourselves by reason. Following them is therefore an exercise of freedom, not a surrender of it, since the will is freed from both natural necessity and the pull of desire.
If reason existed merely to make us happy, instinct would do the job better. So reason's true role must be to produce a will that is good in itself.