How to comprehend "take on"??
The sentence is quoted form Bill Gates 2007 Harvard Commencement Speech, the original words are " In line with the promise of this age, I want to exhort each of the graduates here to take on an issue - a complex problem, a deep inequity, and become a specialist on it."

If the "take on" here means to undertake, to solve, I will be cofused, because it's not in line with the west culture- No one has the right to require somebody to do something without his/her agree, even the president can not, It's rude if you tell someone what things he/she should do. In Bill Gates' speech, he exhort/advise the graduates to take on the issue, without asking the graduates' will before, how does Bill Gates know the graduates are willing to take on the issue? Isn't it decent by saying this?
But in another word, it's Bill Gates' speech, unlikely mistakes would happen, and that is where puzzles me.
I hope someone of kind heart will give me a proper explanation.
Sincerely~

Question

How to comprehend "take on"??
The sentence is quoted form Bill Gates 2007 Harvard Commencement Speech, the original words are " In line with the promise of this age, I want to exhort each of the graduates here to take on an issue - a complex problem, a deep inequity, and become a specialist on it."

If the "take on" here means to undertake, to solve, I will be cofused, because it's not in line with the west culture- No one has the right to require somebody to do something without his/her agree, even the president can not, It's rude if you tell someone  what things he/she should do.  In  Bill Gates' speech, he exhort/advise the graduates to take on the issue, without asking the graduates' will before, how does Bill Gates know the graduates are willing to take on the issue?  Isn't  it  decent by saying this? 
 But in another word, it's Bill Gates' speech, unlikely  mistakes would happen, and that is where puzzles me.  
I hope someone of kind heart will give me a proper explanation.
Sincerely~

Answer

You are correct in saying that "take on" means to undertake (or to assume responsibility for).

However, in this context, Bill Gates does not require the students to do anything.

He is simply encouraging each student to choose an issue or problem that resonates with them, and dedicate themselves to solving it.

The choice of which issue to "take on" is up to the student.  The line is meant as an inspirational call to action, not a command or demand.

Answer

Just to follow up on Tyron’s comment. It’s not unusual in commencement speeches for the speaker to urge the graduates to do (or not do) something, and often in language more direct than Gates’. Compare, for example, Steve Jobs’ inspiring string of imperatives in this short extract from his commencement address at Stanford University in 2005:

“Your time is limited, so don't waste it living someone else's life. Don't be trapped by dogma — which is living with the results of other people's thinking. Don't let the noise of others' opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition.”