" Of all the work that is done or that can be done for our country, the greatest is that of  educating the BODY, the MIND, and above all the CHARACTER, giving spiritual and moral training to those who in a few years are themselves to decide the destinies of the nation." 

Theodore Roosevelt  

 What this is saying is that when you've done the work for this country you can show others what that work showed you.For example lets say that you do something good for your country and it took you a while for you to accomplish that work, then you finally say you are done with what you've been wanting to accomplish and people ask what what did it take for you to accomplish it or what did the work showed you. You say is it showed me how to educated my body into doing whats right and whats wrong, it taught me how think calmly on what to do and not over think many things when their not that important to over think, but out of all it showed me my character and who i really am and how i really acted it showed me how to gain dignity and how to have respect for others. Also that it is saying that you are giving spiritual and moral training to those who are going to accomplish what you've accomplished and that are going to decide the nation's destiny. You are also showing other people how to help others and be a good person, how to gain character and how to respect others.