Charles Ellicott Commentary Exodus 21:6

"then his master shall bring him unto God, and shall bring him to the door, or unto the door-post; and his master shall bore his ear through with an awl; and he shall serve him for ever." — Exodus 21:6 (ASV)

His master shall bring him unto the judges. A formal act was necessary. The State must sanction the passing of a citizen into the slave condition, and so the “judges” were called in. The change was to be made by a significant ceremony. To mark that from then on the volunteer slave became attached to the household, he was to be physically attached to the house by having an awl forced through his ear and then driven into the door or doorpost. Therefore, “opening the ear” became a synonym for assigning a man to the slave condition in perpetuity (Psalms 40:6). The word used for “judges” is ha-Elohim, “the gods,” or “the exalted ones,” which has the same sense in Exodus 22:8-9.