Then the Lord said to Moses, "Make a bronze basin, with its bronze stand, for washing. Place it between the Tent of Meeting and the altar, and put water in it. Aaron and his sons are to wash their hands and feet with water from it. Whenever they enter the Tent of Meeting, they shall wash with water so that they will not die. Also, when they approach the altar to minister by presenting an offering made to the Lord by fire, they shall wash their hands and feet so that they will not die.As you can imagine, the priests had need to clean up after their sacrificial duties, however per the Lord's command they were to clean themselves before they began the Lord's work as well. This cleansing was not so much an actual cleansing as it was a symbolic cleansing. This ritual washing represented their purified life of service to God in the Tabernacle.
~ Exodus 30:17-21
This cleansing was necessary because as humans with our sin nature we are not pure and holy to stand before the Lord or to do His work.
They made the bronze basin and its bronze stand from the mirrors of the women who served at the entrance to the Tent of Meeting.
Some believe it is significant that we can see our reflection in the water which cleanses us from our sin.
Jesus cleanses the church (his bride) "to make her holy, cleansing her by washing with water through the word and to present her to himself as a radiant church, without stain or wrinkle or any other blemish, but holy and blameless." (see Ephesians 5:26-27)
By washing ourselves in God's Word we purify ourselves and enable ourselves to do His work, holy and pure. Continually washing ourselves in His Word keeps our focus on God, not on the world.