Mencius - Book 5, Part 1, Chapter 7B

'T'ang thrice sent messengers to invite him. After this, with the change of resolution displayed in his countenance, he spoke in a different style, "Instead of abiding in the channeled fields and thereby delighting myself with the principles of Yâo and Shun, had I not better make this prince a prince like Yâo or Shun, and this people like the people of Yâo or Shun ? Had I not better in my own person see these things for myself?

'"Heaven's plan in the production of mankind is this: that they who are first informed should instruct those who are later in being informed, and they who first apprehend principles should instruct those who are slower to do so. I am one of Heaven's people who have first apprehended; I will take these principles and instruct this people in them. If I do not instruct them, who will do so?"

'He thought that among all the people of the kingdom, even the private men and women, if there were any who did not enjoy such benefits as Yâo and Shun conferred, it was as if he himself pushed them into a ditch. He took upon himself the heavy charge of the kingdom in this way, and therefore he went to T'ang, and pressed upon him the subject of attacking Hsiâ and saving the people.
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.