It was necessary to ensure that only true Israelites lived within Jerusalem. There follows a list of names of all the families of those who came back from Persia to Jerusalem under the leadership of Ezra, some thirty years before the time of Nehemiah. These were among the ones who helped him build the wall….
He is not only giving credit to them but is also recognizing that they will be responsible to carry on what he has begun. So having appointed leaders who would succeed him–men of integrity, courage, and faithfulness–he now sees to it that their followers are also true Israelites.
The spiritual application is that we need to know that we really belong to God. You will never be a successful servant of Christ nor ever faithfully work for Him and serve Him until you are assured that you know Him and belong to Him. This is not only necessary for leaders but for the common people as well. We all need to know our spiritual pedigree; otherwise, our service will be weak and largely ineffective.