In reading some of the commentaries on these two chapters I learned that as a general rule the kings of the Persian empire did not permit cities within the empire to have walls around them. Walled cities made it easier for local strongmen to put their own armies inside the walls and rebel against the rule of the king.The Persian kings were constantly engaged in putting down rebellion in various parts of their empire and sometime it cost them their own lives when (as happened with Ataxerxes' father Xerxes) men close to them took advantage of their relationship to assassinate them. It was much easier for the king to send in troops from neighboring loyal provinces to put down rebellion and exert authority over a city if there was no wall that had to be breached. In Ezra we see the Samaritan troops easily entering Jerusalem to stop the rebuilding of the wall under orders from King Ataxerxes. We also know that the Persian kings were constantly engage
But God strengthens Nehemiah's influence with the King so that he has reverses this long-standing policy and authorizes the rebuilding of the wall around Jerusalem. It's no wonder that Sanballat, Tobiah and Geshem are disturbed by this change in direction and find it hard to believe that Nehemiah is being trusted to rebuild the wall and remain loyal.
It seems to me that Nehemiah's unshakable faith in God's call to this task strengthened both his reliance on his close relationship with the king so that he fearlessly brushes off the attempts to threaten both the builders and his own life and leadership. Which once again reminds us that God not only calls us to specific work for his Kingdom but also works through other people to support us in our tasks.