Our Gemara on Amud Aleph describes the ritual for expanding the boundaries of the Temple and Jerusalem to share the same holiness:

The same halacha applies to one who enters the original Temple courtyard and the later addition, because the additional section is sanctified with the full sanctity of the Temple courtyard.

The mishna states: Additions to Jerusalem or the Temple courtyards require a special body comprising the king, a prophet, the Urim VeTummim, and the Sanhedrin of seventy-one judges, along with two thanks-offerings and a special song. Once completed, the addition gains the original courtyard’s sanctity.

The sanctification process involves four elements: the king, a prophet, the Urim VeTummim, and the Sanhedrin. The Urim VeTummim, similar to prophecy, provided divine guidance via ruach hakodesh, was below prophecy but above bas kol (see Ramban, Shemos 28:30).

Sefer Daf al Daf debates whether the Urim VeTummim in this ritual were merely ceremonial vestments or used to consult God for permission. The Rambam (Laws of Beis Habechira 6:11) suggests the former:

We may not expand the limits of Jerusalem or the Temple Courtyard unless receiving the verbal consent of the king, verbal consent of a prophet, the Urim VeTummim, and the verbal consent of the Sanhedrin of 71 judges.

Ramban uses “verbal consent” (al pi) for the king, prophet, and Sanhedrin but omits it for the Urim VeTummim, implying a ceremonial role.

I will add a logical proof as well. Ancient Jewish governance, while not identical to modern systems, also had a division of powers for checks and balances. The king represented the people’s will, the Sanhedrin ensured legal and halachic validity, and the prophet provided divine and moral guidance. Since prophecy surpasses the Urim VeTummim, the prophet’s presence likely suffices for divine approval, making the Urim VeTummim’s role ceremonial, akin to the Cohen Gadol’s vestments in Temple service.

But if so, what do the Urim VeTummim represent, given the king (people’s will), Sanhedrin (law), and prophet (divine blessing) are covered? Since they were part of the Choshen Mishpat, bearing the Twelve Tribes’ names (Shemos 28:21), they likely symbolize the unity of the Jewish people, finalizing the expansion with national cohesion.