How do you motivate yourself to do heroic good on rational grounds as opposed to spiritual grounds?

Excerpts from the Gifford Lectures Brand Blanshard
 
https://www.giffordlectures.org/books/reason-and-belief

BEING MORAL AND BEING RATIONAL

 ‘But what of the vast motive power of religion? Is that now to be lost, and deliberately? Surely a pale and consumptive “sentiment of rationality” is not going to propel any Franciscans out among the lepers or any Xaviers across the sea. These men were not living by the wan light of their own thought, but by another kind of light entirely; they were obeying what for them was the will of God, and their everlasting destiny hung on whether they heeded that will or not. The drive wheel of their lives was attached to a powerful motor behind the scene, and it is idle to suppose that the power will still be available when the connecting belt has been broken.’ This is fair criticism. But it raises two very different questions: One is: Is not the motive of being reasonable quite different from that of being moral? and can such a motive supply the driving force necessary to the good life?

As for the first question, the motive of life according to reason is actually purer morally than the religious motive itself. To do something because it will achieve an eternal reward or avoid an eternal punishment is not acting morally at all; the moral man acts in a certain way because he thinks it is right, not because it is self-serving. If a man acts as he does because he believes God wills it, his motive is higher, but still not the highest. What is that highest motive? Presumably the motive that would lead God himself to will it. But he cannot will it because he wills it; that makes no sense. He must be presumed to will it because it is right, and that is what should move man too.

But is not the idea of being moral one thing, and the ideal of being rational quite another? Certainly a man may consider what it is reasonable to do in buying a house or settling a bill without feeling any moral problem at all; and equally certainly the good man may be in no sense an intellectual. It remains true, however, both that the objectively right act is the one that a fully instructed reason would approve, and that the subjectively right act is the one approved by such insight as we can now command. The view that moral action means reasonable action has been accepted by thinkers as far apart as Kant on the one hand and Sidgwick and Moore on the other. I do not myself accept Kant's way of using reason in morals because it seems to me too formal and abstract, and hence too insensitive to the circumstances of the particular case. Reason tells us that we ought not to lie or steal, but to make these into universal mandates admitting no exception would in marginal cases demand what is absurdly irrational. The application of reason to conduct is made, I think, in a different way. In determining duty the main office of reason is (a) to develop in thought the values in terms of fulfilment and satisfaction that are involved in the actions proposed, and (b) to balance the net goods against each other.4 If the attempt to be reasonable in this sense were fully successful, one would see and do what was right; the right and the rational would coincide. The ideal of rationality in conduct is thus also the moral ideal, though with emphasis now placed on the instrument of its achievement.

It must be admitted that the foresight and the maturity of judgement necessary to see with certainty what is objectively right are not granted us, and that we must make do with such limited vision as we have. Does not that mean that ‘rationality’ in practice is, after all, a state of anarchy in which each man does what is right in his own eyes? The appeal to reason is a sorry guide if every prophet with a new nostrum can preface his sales talk with ‘it stands to reason’.
There is very little force in this criticism. It offers the unreal alternative of perfection or nothing. Reasonableness, to be sure, is an infinitely exacting ideal, which we shall never fully realise, but this does not mean that we are all equally far removed from it, or that we cannot move nearer it if we try, or that if we do try, we shall not reach fuller agreement about what it requires. In any but benighted communities there are some persons who stand out above others in their concern for dealing justly with their fellows and whose counsel is sought for its fairness and ripeness of judgement. And to say that persons who prize such things do not tend to agree as they cultivate them is virtually to deny that there are objective standards at all.

To be sure, there are persons who pride themselves on this denial as a mark of sophistication. There has been much talk in recent years about ethical and cultural relativism by persons who think they can dispose of objective standards merely by pointing to diversities of custom. They would not argue this way in other fields. They would not hold that since masses of Chinese people believe that the moon goes into eclipse because a celestial dog bites a piece out of it, while Western astronomers deny this, there is no such thing as an objective standard in astronomy. They would scout the idea of a Russian and an American physics, or of a French and an Indian chemistry, each contradicting the other but with equal claims to validity. There is simply physics or chemistry, with one universal standard of truth, to which place, time, and nationality are irrelevant.

I believe that, similarly, there is one universal standard of morality, set by the fundamental needs, and therefore ends, of human nature. This standard is at work in men's minds implicitly long before it is given explicit shape; its demands become firmer and clearer as it is acted upon, and more generally accepted as social intercourse widens. That its existence is really recognised is attested by such bodies as the United Nations and the World Court, which assume that when a protest is brought before them in the name of justice the term has a common meaning, and that with patience and good will a rational judgement may be achieved. It is true that reasonableness in morals is more difficult and elusive than reasonableness in mathematics; emotions are more deeply engaged and the appraisal of human values calls for richer resources of imagination and sympathy. Reasonableness in the concrete is indeed infinitely and impossibly difficult. Fortunately it is not one's duty to be infinitely and impossibly rational. It is one's duty only to be as reasonable as one can. If even that were seriously accepted, the world would be strangely different tomorrow morning.

MY NOTE:

If somebody is hurt needlessly then why care why it is immoral? The thought of causing such pain should put you off causing it. Paradoxically morality should and will say that is enough. Morality is paradox and that is fine. Life is riddled with paradox.

Kantian ethics, God ethics and Utilitarian ethics tend to leave what you need and want out.  What matters is the principle and God or the other person.  This unnatural side can make those moralities liable to fail.  How moral is a morality that cannot offer you something of what you want as well?  Surely morality is to be practical!

Some say that you need reason to work out what seems to be the best thing to do.  Some say that reason does not fit into nature which means it comes from the realm of spirit and God perhaps but not nature.