This song was chosen because it has great messages in it. Here are some of those messages:
You can be anything you set your mind to. There are no limitations to what you can achieve.
If anyone says you can't, take that as a challenge to prove them wrong.
Some people think it is impossible to accomplish their dreams. That's only true if they don't try. If they try they will surprise not only themselves but everyone around them. The effort alone makes you stronger.
Never give up, always do your best, strive to be who and what you want to be. If you don’t succeed right away, try a new approach.
Anyone can reach goals if they try, persevere, show great effort, and believe in themselves.
All the jobs listed in the song (teachers, politicians, preachers, leaders, etc) will not give you fame and fortune, but they are jobs where you have the possibility to positively impact so many people's lives and to always be remembered as those who changed the world.