Our brand of democracy is hard. But I can promise that a year from now, when I no longer hold this office, I'll be right there with you as a citizen - inspired by those voices of fairness and vision, of grit and good humor and kindness that have helped America travel so far.

This quote is saying that the system of democracy (or government based on the people’s vote) in the United States is difficult, but that even when the speaker no longer holds their office, they will still be involved in the community and be inspired by the people within it who demonstrate fairness, imagination, determination, good humor, and kindness. They are also saying that these qualities have allowed America to be as successful as it is now.