What is a kohen?
A kohen is a Jewish priest by birth and of direct patrilineal descent of Ahron HaKohen. The kehuna (priesthood) in Judaism is passed down patrilinealy -from father to son, provided the son is not the product of a relationship restricted to the kohen. Once born a kohen, the kohen remains so for life and passes the kehuna on to his sons. It is often said that the kehuna is not optional in terms of it’s restrictions (such as becoming impure to the dead, marrying a divorcee etc.), but is optional in terms of it’s benefits, meaning the kohen has the right and option to forego a kehuna privilege. The torah and chazal place numerous restrictions on whom the kohen may marry, where only those permitted marriages produce the “kosher” kohen fit to perform those services and commandments a kohen is meant to perform. Today, there are thousands of religious kohanim worldwide who are proud descendants of Ahron HaKohen and are happy to perform those mitzvot that apply to kohanim, including Nessiat Kapayim, being there for your Pidyon HaBen ceremony and more.
Compared to the heavenly angels
Bamidbar Rabbah details the flag layout of each shevet (tribe), according to the medrash the flag of Shevet Levi looked like this
Sefer HaBahir presents parallels between the 24 משמרות of malachim -heavenly angels- and the 24 משמרות הכהונה – and this comparison is truly amazing. In the days the בית המקדש stood, eyewitnesses to the kohanim’s service in the בית המקדש made this comparison for reason it was clear that the holy spirit of הקדוש ברוך הוא is there with the kohanim when doing their service. It is said that yeshivot and talmud torah’s would be established in yerushalayim since the kohanim doing their service produced an enhanced atmosphere and aura of יראת שמים that would boost the torah students capacity in their torah-studies. Complimentary inborn character traits are telling signs of the kohen, the most dominant being that of חסד -“kindness”. This and other traits are discussed in our article Character traits of the kohen.
Kohanim are in fact members of Shevet-Levi, and are often referred to in the torah as הכהנים הלויים the kohanim the Levites. The talmud cites Rabbi Yehoshua ben Levi who counted 24 places in the torah where the kohanim are called levi’im.