The high priest also wore a golden Forehead-Plate; a Tunic, which he wore under his Robe; a Sash, which he tied around his Robe; and a Turban. The ordinary priests wore tunics, sashes, and hats. Both the high priest and the ordinary priests wore knee-length trousers under the rest of their uniform. As part of the rituals that would install the priests in their office, Moses had to anoint Aaron and his sons, as well as some of the sacrifices, with olive oil compounded with spices according to a specific formula.
Holy vs. Secular Intellect
וְלָקַחְתָּ אֶת שֶׁמֶן הַמִּשְׁחָה וְיָצַקְתָּ עַל רֹאשׁוֹ וגו': (שמות כט:ז)
[G‑d told Moses,] “You must take some of the anointing oil and pour it on [Aaron’s] head. Exodus 29:7

The oil was smeared in the form of the Greek letter lambda (Λ), which is the angled form of the Hebrew letter kaf (כ), the initial of the word for “priest,” kohen.

Whereas the Greeks believed human intellect to be the highest arbiter of truth, Judaism asserts that G‑d’s supra-human intellect is the source of truth. These two worldviews are sometimes at odds, for the Torah’s demands sometimes transcend human intellect. This is why the followers of Greek philosophy fought the Jews and the Torah in the struggle that resulted in the miracle of Chanukah. It therefore seems hardly appropriate to introduce a Greek symbol into the installation rites of the Tabernacle, the spiritual center of Judaism!

The reason why this was done is because G‑d’s intellect, as it is expressed in the Torah, is meant to sanctify human intellect. This is why specifically the Greek form of the letter kaf was used in the rites initiating the Tabernacle.1