Ezra and God's people were given the authority to restore God house.
In Ezra 8: 15 Israel was gathered for the work but there was no one from the tribe of Levi. In verse 18 a Levi was sought out and found to fulfill the ordinance of God. This incident of the need to find the missing tribe of Israel is a good example of obedience.
God's word is not to be modified but it is to be obeyed. Ezra in his mind could have said "lets move on with out the tribe of Levi represented" but this work was not his own work to make decisions on his own. The work that Ezra had and the work that we have today is the work of God. "As my father sent me even so i send you"," I must be about my father's business," "I am the author and the finisher of your faith". John 14:20 At that day ye shall know that i am in my father, and ye in me, and I in you. Matt 28:18-20 ..... All power is given unto me in heaven and in earth. Go ye therefore, and teach all nations baptizing them in the name of the farther, and of the son , and of the Holy Ghost. teaching them to observe all things whatsoever I have commanded you : and lo; I am with you always, even unto the end of the world. Amen.