This chapter begins an accounting of all those who headed back to Jerusalem after the Babylonian captivity. The Persians were meticulous note takers, even to the point of counting how many from each family left the region now under Persian control to head to Jerusalem, also under Persian control.
I love the detail about those priestly families whose records over time had been lost and so they were no longer considered clean. They were considered no longer in the priestly class so could no longer serve the priestly duties. There was nothing about ordination, it was all about in what family you were born. It just takes us to a place where we do have to recognize that this was a sort of caste system. This system was one where certain families had certain responsibilities and that could not be changed.
Of course that is no longer the case in the church. It is not a family run business, but there are certain responsibilities that certain people need to have.