Exodus 28

Upon receiving priesthood authority to administer in the administration and ordinances in the tabernacle, the Lord instructed -

"...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.
2 And thou shalt make holy garments for Aaron thy brother for glory and for beauty.
3 And thou shalt speak unto all that are wise hearted, whom I have filled with the spirit of wisdom, that they may make Aaron's garments to consecrate him, that he may minister unto me in the priest's office.
4 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."  (Old Testament | Exodus 28:1 - 4)

It is my understanding that the ephod was an apron.  And apron in my mind is a symbol of work and service.  As these brethren put on these priesthood robes, including the apron, it meant they were servants of God and were to administer and minister in priesthood work.