Not long after separating from Judaism, Christianity developed a clerical class responsible for shepherding the people, officiating at services, and conducting the sacraments. The clerical class of presbyters came to be called priests. However, the various priesthoods of Christendom are different from the priesthood of the Bible. The biblical priesthood is unrelated to the priesthood that operates within Christianity.
The Hebrew word for "priest" is kohen (כהן). If you are Jewish and have a last name like Cohen, Kowen, Kahan or Koen, you are probably a descendant of Moses' brother Aaron and his sons. Your ancestors served as priests in the Tabernacle and in the Temple in Jerusalem.
Then bring near to yourself Aaron your brother, and his sons with him, from among the sons of Israel, to minister as priest to Me—Aaron, Nadab and Abihu, Eleazar and Ithamar, Aaron's sons. (Exodus 28:1)
In the Bible, only the descendants of Aaron could be priests. They were born into the position. Priests did not undertake vows of celibacy. Instead, priesthood was passed on through families. The descendents of Aaron have attempted to preserve their family lineage through the generations. The priests are a special family group within the Jewish people. Most Jewish communities have several families that belong to the priesthood.
Priests and rabbis are not the same. A rabbi is someone who has gone to rabbinical school (yeshivah) and received rabbinic ordination by an official ordaining body within Judaism. Any Jew can become a rabbi, and a single Jewish community often has many rabbis.
To this day, the priests retain their priestly status in Judaism. Descendants of the Aaron are still subject to special restrictions and laws of Torah that applied to the biblical priesthood. Moreover, the priests enjoy special privileges in the synagogue and serve in certain ritual functions. For example, if a priest is present on Sabbath, he is given the first opportunity to read from the Torah scroll. At the end of the Sabbath prayers, he is called up to offer the priestly blessing over the congregation. Priests are also responsible for ritual functions in the community like the redemption of firstborn sons.
Despite these modern functions, the Aaronic priesthood isn't what it used to be. In the days when the Tabernacle (or Temple) stood, the priesthood was a crucial component in the service of God. They were responsible for worship services. They handled the sacrifices and took care of the altar fires, lit the menorah, burned the sacred incense, baked the bread of the Presence and did all the service of the Tabernacle. They carried out the divine service on behalf of the entire nation of Israel. Moreover, they were responsible for teaching the people Torah.
The priesthood illustrates our relationship to God. Like the common Israelite in the days of the Tabernalce, we are unable to enter directly into the presence of God. Instead, we need a go-between—an intermediary. In the Tabernacle and the Temple, the intermediaries were called priests. They facilitated the relationship between God and the people of Israel. In a similar way, we disciples of Yeshua regard our Savior as our intermediary with God. He is the go-between who acts as a priest for us in the heavenly Temple. However, the priesthood of our Master is a spiritual one, and does not supplant the worldly, eternal priesthood promised to the sons of Aaron.
The priests have been out of work since the destruction of the Temple, but they could be called back to work if the Temple was ever rebuilt. The priests today await the rebuilding of the holy Temple in Jerusalem, when they will be called up for duty. One day they will be. According to the prophet Jeremiah, God's promise to restore the Aaronic priesthood is inseparably linked with his promise to send the Davidic Messiah:
Thus says the LORD, "If you can break My covenant for the day and My covenant for the night, so that day and night will not be at their appointed time, then My covenant may also be broken with David My servant so that he will not have a son to reign on his throne, and with the Levitical priests, My ministers." (Jeremiah 33:20-21)