What was the "Urim ve'Tumim"?
), via which Hashem created three hundred and ten worlds (which every Tzadik will merit in the world to Come - See Mishnah at the end of Uktzin - and which is engraved on the Even Shesiyah (the stone on which Hashem founded the world), with which He stopped up the great deep at the time of the creation - and whoever mentions it in time of trouble will be saved (Targum Yonasan).
If the Nochrim are able to divine the future using the powers of Tum'ah, how much more so are Yisrael able to do so using the power of Kedushah; since Hashem created the two powers pitted one against the other (Rashbam).
What is the significance of the name 'Urim ve'Tumim'?
Rashi and Targum Yonasan: Because it caused the Choshen to illuminate its message (Urim) and enabled the Kohen Gadol to arrive at the accurate conclusion' (Tumim). 1
Ramban: The Urim ve'Tumim 2 comprised two sets of Holy Names of Hashem - one that caused the relevant letters 3 to light-up (Urim); the other, that enabled the Kohen Gadol to read the letters correctly (Tumim), even though they did not necessarily appear in the order that they needed to be read. 4
Da'as Zekenim (16), Hadar Zekenim (27:21): Urim refers to countries - "Ur Kasdim", "ba'Urim Kabdu Hashem" (Yeshayah 24:15). Tumim refers to boundaries -the boundaries of each Shevet was written inside, and the lottery to divide Eretz Yisrael came out like in the Choshen, and no one could protest.
Yoma, 73b: They are called "Urim" because they illuminate their message and "Tumim" because they always actualize their words. 5
Yerushalmi, Yoma, 4:3: They are called "Urim" because they shine on behalf of Yisrael, and 'Tumim", because they show Yisrael the way (of Midos). 6
In the time of the second Beis-ha'Mikdash, the Kohen Gadol wore the Choshen Mishpat because it was one of the eight Begadim that he was obligated to wear, even through it did not contain the Urim ve'Tumim (which were hidden together with the Aron ha'Kodesh). Refer also to 28:30:4.2:1*.
Which constituted a level of prophecy that was lower than Nevu'ah, but higher than the Bas Kol that they employed in the time of the second Beis-ha'Mikdash (Ramban).
That spelled the answer to the questioner (Ramban).
See Ramban, who elaborates.
As opposed to Nevu'ah, which, although is a higher level of prophecy, can be reversed
Why does the Torah insert the 'Hey' at the beginning of "ha'Urim ve'Tumim", even though they have not been mentioned before?
Something that it generally does not do unless it has already been mentioned previously - such as "ve'es ha'Mishkan Ta'aseh" (Terumah, Sh'mos 26:1), which was mentioned earlier there in 25:8 (Ramban).
Why did Hashem insert "Vehayu al Leiv Aharon ... ?
What is "Mishpat B'nei Yisrael" referring to?
Rashi #1: It is referring to the judgments of Beis-Din that the Urim ve'Timim are coming to settle
This is also how Targum Onkelos and Targum Yonasan seem to explain the Pasuk.
Why did Hashem not place "Venasa Aharon es Mishpat B'neo Yisrael ... " tofether with "Venasa Aharon es Sh'mos B'nei Yisrael" in the previous Pasuk?
Oznayim la'Torah: Because the Names of Yisrael and their judgment are two not directly connected issues, each of which Aharon carried on his heart independently. 1
Oznayim la'Torah: As we see in the second Beis Hamikdash, when the Urim ve'Tumim was missing and Aharon carried the names of Yisrael exclusively.
Why, in the previous Pasuk, did Hashem say "be'Vo'o el ha'Kodesh, and here "be'Vo'o Lifni Hashem"?
Oznayim la'Torah: Because the Urim ve'Tumim could also be employed outside the Beis Hamikdash
Oznayim la'Torah: Bearing in mind "M'lo Chol ha'Aretz Kevodo".
What are the implications of "Tamid"?
Oznayim la'Torah: Another advantage of the Urim ve'Tumim over Nevu'ah 1 is that whereas a Navi cannot prophecy at will, 2 The Urim ve'Tumim would always answer on behalf of Yisrael when its advice was needed.
When did Moshe actually place the Urim ve'Tumim inside the Choshen?