It must have seemed odd to Moses to now be annointing his older brother -- who had been in Moses' shadow -- as high priest. Aaron's sons ruled over Moses' sons. Yet Moses was a faithful man, following hard after God.
There is a lesson in there for all Christians, I think, about the importance of humbling ourselves to God's will. Pride is a human emotion that can spoil God's plans if we do not make it subservient to Him.