“Even if, by some especially unfortunate fate or by the niggardly provision of stepmotherly nature, [the good will] should be wholly lacking in the power to accomplish its purpose; if with the greatest effort it should yet achieve nothing, and only the good will should remain (not, to be sure, as a mere wish but as the summoning of all the means in our power), yet would it, like a jewel, still shine by its own light as something which has its full value in itself.”