Ordination
Dress is but one issue calling for clarification and revision. With robes went authorisation. By the time Exodus was taking shape priesthood had something of a chequered history. Levites still enjoyed a special relationship but not a monopoly, and the boundaries defining the office were less clear. Some evidence suggests that some were descendants of the old Canaanite priests, some had allied themselves to the monarch, and some were actually attached to the royal household, a relationship which then morphed into a natural allegiance, with a strong tendency to imitation (what was good for the monarch would be good for the priest), much to the chagrin of those prophets who paid a price to maintain their independence.
To appreciate what is going on, first put aside what we understand by ecclesiastical words such as ‘ordain’ and ‘consecrate’. The variety of English translations unfortunately obfuscates the finer points of the Hebrew text, where ‘consecrate’ (Heb ‘make holy’) relates to ‘clean and unclean’ and ‘ordain’ (Heb lit ‘fill the hands’) relates to laying on of hands, a blessing or a gift. Then stand in their shoes and ask yourself what they were they trying to achieve? Mainly, a link to the past (their origins), what has been gained and what lost over the years, and what needs immediate attention for their day.
For a people of faith worship is the focal point. They need a place to meet with one another and with God. The ark encapsulated the idea but is inappropriate for their new situation. Surrounded by temples, they need a Temple, and with the Temple they need leaders ‘set apart from common association‘ (John Gray) — priests probably, or the like. Aaron is history, but they need ‘an Aaron’ (perhaps more than one), identified and authorised, with powers clearly defined and limited, capable of maintaining the worship and the general direction of the faith, keeping the faithful out of trouble (becoming ‘unclean’) and leading them into a wholesome and healthier way of life (‘holiness’).
Once defined those priests need to be consecrated (made whole) and set apart (ordained), possibly with hands laid on, or with hands sufficiently filled, possibly with some symbol of office (the Scriptures maybe) to remind them of their privilege and responsibility.