A priest is a mediator between God and man. More specifically, Jewish priests were the official ministers of Israel and descendants of Moses’ brother Aaron, from the tribe of Levi. Aaron was ordained as Israel’s first High Priest as they journeyed from Egypt to Canaan, and his family subsequently became the official priestly line. The Greek term archiereus (“first priest”) referred to the current or past priest who governed all the other priests as the religious head of Israel. This position is often translated “High Priest” or “Chief Priest.”
A priest was to be set apart for service in all things, from appearance (no physical defects) to family life (wife must be a virgin from Israel). The High Priest’s purification process involved a week-long ceremony of bathing, dressing in specially-made priestly clothes, and being anointed with oil. A priest’s duties included burning incense, tending to ceremonial lamps, ensuring offerings were properly prepared, teaching the Law, and judging court cases. But most importantly, the High Priest would enter the innermost room of the Temple, the Holy of Holies, once each year and offer sacrifices for himself and the people.
The role of priests diminished somewhat over time as they were overshadowed by other religious groups, such as scribes and Pharisees. As well, the role of High Priest was no longer hereditary under Roman rule, but could be appointed or deposed as the current ruler desired.
[Aaron and his sons] will be anointed for an everlasting priesthood throughout their generations.
– Exodus 40:15