Parshas Tetzaveh records the details of how the garments of the Kohen Gadol and the other Kohanim were to be made. Two of these garments were adorned with precious stones, on which the names of the 12 Tribes were engraved.
On the Choshen (breastplate), the names of the 12 Tribes were inscribed on the 12 precious stones, arrayed in 4 rows of 3 stones. The Tribes were inscribed according to the order of their birth.
The other place where the names of the Tribes were engraved, was on the Avnei Shoham – the two onyx stones on the shoulder straps of the Ephod. Each stone bore the names of 6 Tribes. The sages of the Talmud have differing opinions on the order in which the Tribes were listed on these stones.
In the laws of the Temple Vessels, the Rambam describes and depicts the two Avnei Shoham. Initially it seems that the Rambam’s opinion does not reflect any of the opinions in the Talmud. In order to reconcile the Rambam’s view with the Gemara, the commentators explain that the Rambam viewed the Avnei Shoham as one single stone that is merely divided between the two shoulders. The order of names in the Talmud was written across the two stones as they are united.
So whereas on the Choshen each Tribe had their own individual stone, on the Avnei Shoham, all of the Tribes shared the same stone.
The reason that the names were etched into the stones of the Choshen was so that “Aharon will carry the names of Bnei Yisroel on the Choshen... over his heart, when he enters... before Hashem.” Likewise, the wearing of the names on the Shoham stones of the Ephod is so that “Aharon will carry their names before Hashem on his two shoulders as a remembrance.”
The difference in how the names appeared on the two garments, represents the different merits of the Jewish people that the Kohen Gadol would bring before Hashem.
On one hand, we each have our own individuality. These represent our own spiritual accomplishments and strengths. At the same time, we are all part of one people, suggesting a sense of equality. This is the merit of our unity.
Chassidus likens the different manner in which the names were inscribed on these two garments, to the difference between how the Torah passages are inserted into the Tefillin of the head and the Tefillin of the arm.