Isaiah 46 - 50

The Lord GOD hath opened [pierced] mine ear, and I was not rebellious, neither turned away back. - Isaiah 50:5

Piercing of the ear alludes to a procedure. In those days, if you were in debt you were in service until either the debt was paid or the Jubilee year. At that point you would be free to go; however, often by this point, the servant so enjoyed the hospitality of the household that he would voluntarily choose to serve the house for the rest of his life, an awl was used to pierce the ear of the slave to the doorpost of the house, and the person became bonded to the household.