Theodoret of Cyrus
How is it that David, who was not a priest, donned the ephod? The scripture states, "But David wore the ephod." We have noted previously that Aquila referred to the ephod as an upper garment, while Symmachus described it as simply a garment. Notably, upper garments could be both priestly and common in nature. Therefore, it is clear that the revered King David, a man devoted to God, would not have violated the law or taken it upon himself to wear a priestly vestment. Rather, it is indicated by these words that when David led the ark and rode before it, he was not adorned in royal attire but instead wore a sleeveless garment, now known as Arcadian.