mission; assignment; task; duty; role

We will all work together to finish this task on time.

My boss assigned the hard job to me.

It won't be easy to find someone capable of taking his place.

And I know you didn't do this just to win an election. And I know you didn't do it for me. You did it because you understand the enormity of the task that lies ahead. For even as we celebrate tonight, we know the challenges that tomorrow will bring are the greatest of our lifetime: two wars, a planet in peril, the worst financial crisis in a century.

I am charged with an important mission.