From Improving the World (#792) by Rabbi Avigdor Miller
The Gra in his sefer Even Shleimah makes a remark as follows:”A man is created in order to change his nature,” to break his middos ra’os (negative character traits). If he doesn’t do that, then “lama lo chayim — why should he live?” Why should he live!? Why shouldn’t he live? He gives tzedaka (charity), he learns Torah, he does many things.
Let’s say he's an angry man, a hot-tempered person, he doesn’t want to learn how to cool down and become moderate. Or he’s a man who likes to be honored at all times, he wants glory, and he cannot learn sometimes to be second in rank, or third in rank, he only wants to be the top. He has to break that middah, and if he doesn’t break his middos, “lama lo chayim — why should he live?” A man must achieve a transformation of character.
It states in the Chumash when you see your enemy’s ox lying on the road, you should come over and help him unload his animal. Why mention enemy? The Torah wants to emphasize that just because he’s your enemy you have to feel more obligated. Like the gemara says “l’chof es yiztro adif — to bend his nature is more important”…
We live in order to change. It’s important. So if people criticize you, don’t just bridle and be resentful, listen! Maybe there is something to change. There are many people who leave this world and we don’t understand why; what did they do wrong! But we’re listening now to an explanation that will apply to many cases: the people didn’t want to change themselves. You say that’s how I am, that’s my nature. So Hashem says, I am giving you life only for that reason: to change yourself.
You're here “l’saken olam — to improve the world,” and you're part of the world, that’s why you are empowered to improve. And if you refuse, then “lama lo chayim — why should you live?”