God commanded Moses to build an altar made of acacia wood on which to burn incense. The altar was placed in front of the veil above the ark. Aaron was told to burn incense every morning and every evening as an offering to the Lord. Aaron would make atonement annually and place the blood of the sacrifice on the horns of the altar. A tax was collected from every person twenty years and older for the service of the tent of meeting. Priests were cleansed before entering the tent of meeting. God commanded Israel to keep the Sabbath as a covenant with Him. Anyone who did any work on the Sabbath was put to death.