Nehemiah is one of the biggest heroes in the Bible of whom most people have never heard.
70 years after the exiles were allowed to return to the promised land, Jerusalem is still in ruins. The temple has been rebuilt for about 50 years, but no one wants to move back into the city. A few folks live there to support the temple operations, but there isn't a big enough community to make a city work. The biggest drawback is that the wall is broken in many places and there are no gates. Lots of the folks that moved into Judah when the Jews where exiled don't want the city rebuilt as it could threaten their way of life.
Nehemiah arrives and despite very real threats from the locals, he organized and motivates the people in Jerusalem to rebuild the wall. City walls back then were actually 2 walls with several feet of rocks and dirt filled in between them. Despite having to carry weapons while working all day and stand guard at night, they restore the wall and build new gates in only 52 days. This is so fast, the adversaries don't really have time to organize against Jerusalem. This effort not only unifies the inhabitants of Jerusalem into a community, it (and the security of the wall) inspires more people to move back.
Nehemiah returns to his previous job as cup bearer (think chief of staff) for the king for a couple of years before going back to check on Jerusalem. When he returns, those who wrestle with God (Israel) have already strayed. It must have felt like Moses coming down the mountain to find the golden calf. Its a pattern we find over and over again in the Old Testament and in our lives today: peace, sin, repentance, grace.