Numbers 20:29
And when all the congregation saw that Aaron was dead, they mourned for Aaron thirty days, even all the house of Israel. And when all the congregation saw that Aaron was dead, they mourned for Aaron thirty days, even all the house of Israel.
Aaron died and was buried on Mount Hor. He died there because God had said he would not enter the promised land, having sinned with Moses in bringing water from the rock at Meribah. His brother Moses and his son Eleazar went up the mountain with him.
On the mountain his priestly garments were taken from him by Moses and put on Eleazar, because God had appointed Eleazar to succeed him in the priesthood. His death was witnessed only by Moses and Eleazar, his burial was simple, and Moses buried him on the mountain. Those who hold the other account teach that Moses together with the sons of Aaron buried him on the mountain. He was buried on the mountain so the people would not be tempted to make too great ceremony over his body and become guilty of idolatry.
When all the congregation saw that he was dead, all Israel mourned for him thirty days. They mourned because they loved him, despite the sorrows they had caused him. Their grief honored him as a beloved high priest.
While the congregation felt the loss, Moses felt it more deeply because Aaron had long shared his joys, sorrows, hopes and fears. Aaron's death also reminded Moses that his own life was nearing its end. The scene on Mount Hor brings to mind the most striking events in Aaron's life.