Remember the order of events.
Nehemiah is granted permission to come and rebuild the walls and gates from the King of Babylon.
Ezra had tried a few years before to do that, but was unable.
When Nehemiah arrived, there were only a few Jewish people that were there. They were the ones who helped to rebuild.
Once the walls were done, then they were charged with bringing the remaining Jews from Babylon.
Chapter 7 tells us all those who returned. If you remember, we said that God gave us that detailed list to show us that people matter to God.
He could have just said X number of Jew returned. But he made it a point to list all the leaders of the tribes because people mattered to God.
Sometimes when we think about all the believers in all the churches in the world, we might assume that God forgot about us.
But the Bible says not only does God know who you are, but he knows the number of hairs on your head.