For glory and for beauty

And take thou unto thee Aaron thy brother, and his sons with him, from among the children of Israel, that he may minister unto me in the priest's office, even Aaron, Nadab and Abihu, Eleazar and Ithamar, Aaron's sons.  And thou shalt make holy garments for Aaron thy brother for glory and for beauty.  And these are the garments which they shall make; a breastplate, and an ephod, and a robe, and a broidered coat, a mitre, and a girdle: and they shall make holy garments for Aaron thy brother, and his sons, that he may minister unto me in the priest's office.
Exodus 28:1-2,4

The heads of each family were usually chosen as priests but God turned to only Aaron and his sons to serve as priests. Why only Aaron and his sons? That is because God chose them to minister as priests. God set them apart for this role.

They had to wear a different garment that will display the glory and beauty of God. God also gave specific requirements for making the garments.

Through Jesus we have a new priesthood. The old covenant was replaced with the new hence no more blood of bulls and goats. Jesus shed his blood once and for all and we have access to God through Jesus our high priest. 

Whatever garments you wear, you can talk to God through Jesus. Your new dress code can be found in Ephesians 6:14-17