Aaron was tasked with arranging the lamps in the most Holy Place. They were to be arranged to give light in front of the lampstand. The light of God is to be seen as brilliant and holy in all cases.
The Levites were to be cleansed and dedicated. They would be sprinkled with water of purification, shave their bodies, wash their clothes, and thus be clean. They would then bring offerings of bulls as a sin offering. They would then be brought before the whole congregation of Israel. The people would lay hands on them, offer a wave offering, and the Levites would be separated unto the Lord. The Levites were to serve from age 25 to 50. After that they could minister, but do no physical labor.
It is interesting to see the connection between doing things a certain way for the Lord and then being separated unto God for His service. In order to serve in His house, one must be dedicated unto Him and live a holy life. The ceremonial cleansing and dedication was symbolic of a spiritual cleansing, one that we must seek for today as we serve in the house of God. Whether vocationally or as a layperson, we all have a service to perform. We should do that ministry as people of God, separated unto God, and dedicated to His service.