The ability to distinguish between different things is a critically important ability, and it expresses one of man's intellectual facilities, as Chazal said: "If there is no intelligence, where can discernment come from?"
 

In parshat Terumah it is written: "And the Parochet (curtain) will separate for you between the Holy and the Holy of Holies." This is a unique separation, since we are familiar with separation between things which are completely opposite and detached, as it says in parshat Shemini: "to separate between the impure and the pure." And we are also familiar with separation between Kodesh and hol (the Holy and the mundane) but here is a finer distinction - between Holy and Holy -meaning between regular Kodesh and Kodesh HaKodeshim.
 

The Zohar Hakadosh interprets here "Anyone who subordinates himself to a Torah scholar is called Holy, and the Torah scholars themselves are called Holy of Holies. And this secret is hinted at in the verse: And the curtain separated between the Holy and the Holy of Holies." In the Kodesh are the Table, the Menorah and the Altar, but in Kodesh HaKodeshim is the Ark of the Covenant, and in it are the Tablets of the Testimony which embody the holiness of the Torah, and this is a special level of holiness above all the other levels. Korach's error was rooted in misunderstanding this when he said: "as the entire congregation, all of them are holy" – this is indeed true, but he didn't comprehend that Moshe and Aharon are Kodesh Kodeshim.
 

And these are the words of the Rambam at the end of Hilchot Shemittah and Yovel: "The tribe of Levi was set apart to serve HaShem. And not only the tribe of Levi, but any man whose spirit inspires him to separate himself to stand before HaShem to serve Him – behold, he has sanctified himself (and elevated himself to the level of) Kodesh Kodeshim."