He was a Levite of the family of Kohath (Amram father) , and was three years older than Moses. Exo 6:20, 7:7 Both were younger than Miriam
When the time of the Exodus came, God sent Aaron (Exodus 4:14, 27-30) out to meet the returning Moses
He acted as spokesman for Moses (Exodus 4:14-16). Although Moses was the leader, it was Aaron who did the actual speaking to Pharaoh through the events leading to the Exodus, and the crossing of the Red Sea.
Aaron was a faithful servant with his brother, at least at first.
He performed miracles in God's power in the Egyptian court (Exodus 7:10-13, 19-21),
At Rephidim, when Moses overlooked the battle with the Amalekites from a nearby hill with the rod of God in his outstretched hand, it was Aaron and Hur (his brother-in-law, Miriam's husband), who held up Moses' tired arms until Israel's forces under Joshua won the battle (Exodus 17:8-13)
But he also sided with the people in the building of the golden calf (Exodus 32:1-5) For whatever reason, Aaron gave in to the people's demands, and made that now-infamous golden calf for the people to worship (Exodus 32:4). When Moses returned, Aaron was sternly rebuked and was very close to being killed for that incident (Deuteronomy 9:20)
but was forgiven by God after Moses prayed for him.
With his sister Miriam, he criticized Moses because of his Ethiopian wife (Numbers 12:1-10).
He was prevented from entering into the promised land (Numbers 20:12)
Aaron was the first high priest of Israel, appointed directly by God to be the first high priest. He and his sons were consecrated to continue the priesthood through time (Leviticus 8 and 9). In a plain linen uniform he made atonement for the nation and himself (Leviticus 16:1-23).
The function of the high priest on the Day of Atonement (Leviticus 16)
a) The high priest was not allowed unrestricted access into the Holy of Holies (16:2).
Aaron was to remove the ornate high priestly garments, put on a plain linen uniform, and wash himself (16:4d)
b) He enters the holy place having offered a bullock for a sin offering and a ram for a burnt offering (16:3). ).
The bullock is offered for Aaron, since he, also, is a man. The bullock is the highest value offering.
He has to go in alone (16:17) and offer the blood of the animals (16:18,19).
The blood from the bullock is sprinkled on the mercy seat seven times (16:6, 11-14).
e) Aaron was to select two goats and then select (by casting lots) which goat would be slain and which would be the scapegoat (16:5,7,8).
One goat is slain as a sin offering for the nation of Israel (16:9,15,16), whilst the scapegoat is released into the wilderness (16:10). )
The scapegoat is then symbolically made the sin bearer of Israel by the placing of the hands on its head and confessing Israel's iniquities (16:20-22).
i) Aaron changed from his linen uniform to his high priestly garments (16:23-24).
j) It was to occur on the feast of atonement (16:29,30).
Aaron had four sons, the two oldest, Nadab and Abihu, being killed by God (Numbers 3:4), leaving Eleazer and Ithamar to serve in the priestly line.
He died at the age of 123 (Numbers 33:39) on Mt Hor; after his garments were removed and placed on his eldest surviving son Eleazer (Numbers 20:23-29).