Since Nehemiah started praying for his people in Jerusalem, 4 months passed by, and nothing happened. However, he did not waste his time. Instead, he waited. Waiting is different from wasting. In order for Christians to wait (not waste), two things are needed. One is prayer to discern whether it's God's will or personal resolution, and the other is prepare to do actual job. That's what Nehemiah did. He continuously prayed for 4 months to request his king and prepared how and what to talk. That was seen through the conversation between the king and Nehemiah. When he was asked, Nehemiah prayed (v.4) and answered very wisely, referring Jerusalem to the city of his ancestors' graves(v.3). And the gracious hand of God works for those who wait.
It seemed impossible for a Persian king to revoke his decree. And Artaxerxes himself made a decree to stop rebuilding the wall of Jerusalem 13 years ago. There was no possibility for that king to send one of his closest men (cupbearer) to restart the cancelled job. However, the gracious hand of God (v.8) made the impossible possible.
When he face the difficulties inside and outside, Nehemiah was able to go though by the gracious hand of God. His people was heard and saw that God helped him, and they were motivated. To the enemies who mocked and despised, Nehemiah told 'the God of heaven will make us prosper.' Nehemiah did not rely on his king's letter or army, but he relied on the one thing, which was the gracious hand of God.