In the biblical context, the role of the priest is central to the religious and communal life of Israel. Priests were chosen by God to serve as mediators between Him and the people, performing sacred duties and maintaining the sanctity of worship. The responsibilities of priests are outlined primarily in the books of Exodus, Leviticus, Numbers, and Deuteronomy, with additional insights found throughout the Old and New Testaments.

1. Lineage and Selection:
The priesthood was established through the lineage of Aaron, the brother of Moses, from the tribe of Levi. God specifically chose Aaron and his descendants to serve as priests. Exodus 28:1 states, "Bring near to you your brother Aaron and his sons from among the Israelites to serve Me as priests—Aaron and his sons Nadab and Abihu, Eleazar and Ithamar."

2. Duties and Functions:
The primary duties of the priests included offering sacrifices, maintaining the Tabernacle (and later the Temple), teaching the Law, and blessing the people. Leviticus 1-7 details the various offerings and sacrifices the priests were to perform, including burnt offerings, grain offerings, peace offerings, sin offerings, and guilt offerings. These sacrifices were essential for atonement and maintaining a right relationship with God.

3. Teaching and Judging:
Priests were also responsible for teaching the Israelites God's laws and statutes. They served as judges in legal matters, particularly those involving ritual purity and religious observance. Deuteronomy 17:9 instructs, "Go to the Levitical priests and to the judge who is in office at that time. Inquire of them, and they will give you the verdict."

4. Maintaining Ritual Purity:
Priests were required to adhere to strict standards of ritual purity. Leviticus 21 outlines various regulations concerning the personal conduct and physical condition of priests, emphasizing their need to remain holy and undefiled. This included restrictions on marriage, contact with the dead, and physical blemishes.

5. The High Priest:
The High Priest held a unique and elevated position among the priests. He was the only one permitted to enter the Holy of Holies in the Tabernacle or Temple, and only once a year on the Day of Atonement (Yom Kippur). Leviticus 16 describes the High Priest's duties on this solemn day, including making atonement for himself and the people.

6. Vestments and Anointing:
Priests wore specific garments as a symbol of their sacred office. Exodus 28 provides detailed instructions for the priestly vestments, including the ephod, breastplate, robe, tunic, turban, and sash. These garments were not only for glory and beauty but also signified the priest's consecration to God's service. The anointing of priests with oil was another significant aspect of their consecration (Exodus 29:7).

7. New Testament Perspective:
In the New Testament, the role of the priest is redefined through the person and work of Jesus Christ, who is described as the ultimate High Priest. Hebrews 4:14 declares, "Therefore, since we have a great high priest who has passed through the heavens, Jesus the Son of God, let us hold firmly to what we profess." The priesthood of all believers is also emphasized, as seen in 1 Peter 2:9 : "But you are a chosen people, a royal priesthood, a holy nation, a people for God’s own possession, to proclaim the virtues of Him who called you out of darkness into His marvelous light."

The responsibilities of priests in the Bible reflect a profound commitment to serving God and His people, maintaining holiness, and facilitating worship and atonement. These duties underscore the importance of mediation and sanctity in the relationship between God and humanity.