Exodus 19:10. The Lord said unto Moses, Go unto the people, and sanctify them today and tomorrow, and let them wash their clothes.
This was considered a necessary preparation for meeting Jehovah. Pagans have similar ceremonies ill connection with their worship. Roberts says: “No man can go to the temple wearing a dirty cloth: he must either put on a clean one, or go himself to a tank and wash it, if it be soiled; or he must put on one which is quite new. Near the temples men may be often seen washing their clothes, in order to prepare themselves for some religious ceremony” (Oriental Illustrations). Jacob commanded his household to be clean and change their garments when they went up to Bethel to build an altar to Jehovah (Gen. 35:2).