Ezra 2:63
And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and with Thummim. And the Tirshatha said unto them, that they should not eat of the most holy things, till there stood up a priest with Urim and with Thummim.
After the return from Babylon certain returned exiles claimed priestly descent but could not prove it, since their names were missing from the preserved genealogy. The Tirshatha, the governor, ordered that these unverified claimants should not eat of the most holy things, the altar's most holy food. They were barred from eating until a priest with Urim and Thummim could decide whether they were entitled to serve. The matter was thus left for priestly determination rather than human assumption.
The Urim and Thummim were the breastplate oracle, a divine means of seeking God's will by which God revealed His decision. It was treated as the authority for settling the urgent question of priestly recognition. Such an answer through the Urim and Thummim was still understood to be possible in that generation. Yet they were missing from the high priest's breastplate after the return, no priest with them is recorded as appearing, and the practice had fallen into disuse. Their eligibility therefore remained unresolved until divine guidance could be available.
The delay guarded the purity of the priesthood and the sanctuary service.