Final answer:
Kant likens the good will to a jewel because it possesses intrinsic value, shining with unconditioned worth, similar to the beauty of a precious gem. The good will is esteemed for its intention to fulfill duty, irrespective of the outcome, establishing it as an exemplar of our highest moral capacity.
Step-by-step explanation:
Immanuel Kant famously argued that the good will is the only thing that is good without qualification. He compares the good will to a jewel because, like a precious gem, the good will has intrinsic value that is not dependent on its external manifestations or outcomes. According to Kant, the good will shines by its mere intent to perform duty for duty's sake, rather than for what it can achieve; this makes it inherently valuable and unconditionally good. Furthermore, in Kant's view, only through rational, moral action - manifestations of the good will - do we realize our freedom and affirm our human dignity.
Kant's philosophy emphasizes the importance of the intention behind actions rather than their consequences. He introduced the Categorical Imperative, a principle of universalizability where one acts according to the maxim that one would wish all other rational beings to follow. By doing so, we fulfill our duty, which is deemed as the ultimate good, echoing the essence of the good will.
Kant's normative moral theory is built upon the capacity for human reason and our ability to act out of duty. This places us above other living beings who might be driven by impulse, and not rational decision-making. Thus, the good will is reflective of our highest moral capacity and, like a jewel, has a unique and unfading worth.