These
are the garments they are to make: a breastpiece, an ephod, a robe, a woven
tunic, a turban and a sash. They are to make these sacred garments for your
brother Aaron and his sons, so they may serve me as priests. Exodus 28:4
The
garments visually set the priests apart from the others. It was their uniform that gave them authority
over the work they were doing.
It
also needed to be to breathe (linen) since they did hard work and to be able to
be washed since it got messy (blood).
For
the priests, it helped them to know that they were on-the-job, so they slipped
into the role of priest every time they put the uniform on.