There was a special appeal for people to live in the city of Jerusalem. Remember, things were just starting to be put back together again, so they had to come in from the countryside where they were living and where they had their comfort and where they were used to living. But people had to move into Jerusalem in order for it to be inhabited which would prevent marauders from coming in and taking whatever they wanted from the temple and from harassing the one who were working and living in the temple to keep it running. If no one was around then no one would stop them from doing that.
The process was that one out of ten from each of the twelve tribes were to move into the city. Notice that there is a distinction at the beginning where they say in vs.1 that the leaders of the city lived in Jerusalem, but they cast lots so that they could be joined by a representation of the entire nation by having one out of ten come and join them. It is much easier to lead when you are willing to be the one to take part in what you are asking others to do first. If you just ask them to do something but you are not willing to do it, then why should they do it?
It reminds me of Judge Deborah’s general, Barak in chapter 4 of Judges, where he tells her: “If you go with me I will go, but if you will not go with me, I will not go.” It sounds pretty insolent, and in fact Deborah said that she would go but that he would not receive the glory of the victory.
This listing of the families reminds us of how numerous the tribe of Israel was that they could give up hundreds of people and that only represented one tenth. But things seem to be in place for Ezra and Nehemiah to have Jerusalem under control as the city of God once again.