Some priestly families could not find their registration in the genealogies, so they were considered unclean and excluded from the priesthood. They were told not to eat the most holy food until a priest could consult Urim and Thummim. See Ezra 2:62 and Ezra 2:63.
Ezra 2:59–63 pauses the returnee list to address people whose family records could not verify their Israelite or priestly status. Some groups came from specific towns but could not prove their ancestral “father’s houses.” A priestly set also failed to locate their registration in the genealogical records, so they were treated as unclean for priestly service. This unit sits inside the larger census-style roster of returnees in Ezra 2, where names, origins, and numbers establish who belongs to the restored community and how it is organized. After listing many verified families, the text highlights exceptions: people present in the return but lacking documentation.
Ezra 2:59–63 explains an administrative problem inside the returnee roster: some people arrived with the community, but their family records could not confirm their ancestry. The text treats documented lineage as the normal way to establish membership claims and especially to establish eligibility for priestly work.
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Ezra 2:62, then read the surrounding section so the answer stays connected to the passage's flow.
62These sought their register [among] those who were reckoned by genealogy, but they were not found: therefore were they deemed polluted and put from the priesthood.