aaron is the brother of moses... he is the one that was with moses from the time he went into egypt to free the people... all the way to the edge of the promised land... it is from aaron's line that all priests come... he was the first high priest for israel...
it is strange to me.. that he is the one that built the golden calf that the people worshipped while moses was on the mountain getting the 10 commandments... he was not punished by God for this act... another time, him and miriam their sister rebel against moses because he has married a cushite woman... miriam becomes covered in leprosy... aaron does not... moses intercedes for miriam and she is healed and allowed back into the camp after 7 days.. but why didn't aaron get punished too?
there were great rituals about what he could or could not do.. what he could or could not eat... rituals about the sanctuary tents... rituals of cleansing and of purification to make him holy enough that he would not be destroyed when he stood before God to offer up the different offerings the people gave to the Lord..
aaron's two oldest sons were consumed by fire because they tried to offer up to God 'strange fire'.. now I don't really know what strange fire would mean.. but because everything was laid out very clearly about what could or could not be done.. I would guess they knew that what they were doing was wrong... aaron was unable to mourn his sons because he is in the service of God as high priest... that would have made him ceremonially unclean.. so he had to not mourn them...
he had two more sons who then became the sons that worked closely with him along with the entire levite tribe..
when the people are complaining over and over and over and over... this particular time for not having water... God tells moses to speak to the rock... moses whacks the rock and the water comes out... God determines that moses had taken His glory in his anger... moses and aaron are both punished at this time.. neither of them will ever enter into the promised land...
after aaron dies, his son eleazar becomes the next high priest... aaron is mourned for 30 days after his death...