Joshua - Chapter 23
You Know, I Don't Read These Synopses for Mussar...
At age 110, Joshua realized that he wouldn't live much longer, so he gave words of encouragement to the Jewish people. He reminded them of all Hashem did for them and urged them to be strong in their observance of the Torah.
Joshua restated the prohibition on intermarriage, found in the Torah in parshas Va'eschanan. If the Jews intermarry, Joshua cautions them, Hashem will cease to drive out the Canaanite nations. Just as G-d has brought about every good thing He promised, if the Jews turn their backs on Him, He will bring about all the punishments about which He warned them.
Really, Joshua should have lived to 120, the same as his mentor, Moses. Additionally, like Moses, Joshua should have maintained his youthful vigor, yet we see this is not the case. We are told that this is because, as great at he was, Joshua did not fulfill his potential. He could have done (should have done!) an even better job in conquering the land. If a great leader like Joshua, who is favorably compared to Moses, fell short of his potential and is held responsible for it, how much harder should we "average" people work on meeting our potentials!