The Washing With Water (Exodus 29:4).
“And you shall bring Aaron and his sons to the door of the Tent of Meeting,, and you shall wash them with water.”
The washing with water is always preparatory. Water alone is never said to ‘cleanse'. Its purpose is the removal of ‘earthiness' preparatory to what follows. In days when washing was not a favoured occupation it was seen as very necessary before approaching God. The taint of earthiness that clung to men must be removed (as in the case of their having to wash their feet - Exodus 30:19). They could not wear the holy garments until all trace of earthiness was removed.
It is noteworthy that none can enter the Tent of Meeting until the whole process is completed. It was no light thing to enter the Sanctuary. Assuming that the new Tent of Meeting, the Dwellingplace, is indicated this must occur after the Tabernacle has been made and erected.
This is a reminder that when we enter into prayer our first act should be to ensure cleansing from current sins. We must not enter God's presence ‘unwashed', for He is holy. But washing with water did not indicate cleansing from sin to Israel, it indicated the removal of earthiness prior to cleansing.
Washing with water was a practise common to many religions. The Egyptian priests engaged in constant washing with cold water from head to foot, twice a day and twice every night. It was the significance that often differed. To Israel it signified the removal of earthiness, often preparatory to cleansing. It is never said to cleanse in itself. David in Psalms 51:2; Psalms 51:7 probably has in mind the Water for Purifying (Numbers 8:7; Numbers 19:9-20) which was water treated with the ashes of a heifer and applied with hyssop (Numbers 19:18). David felt like a leper. Although it may be that as a king used to bathing (not something common to all) he also saw verse 2 in terms of being washed clean by repentance (Isaiah 1:16).