Exodus 21:5 gives the same law of the servant choosing to stay because he loves his master.

Exodus 21:6 details the ear-piercing ritual that follows the servant's declaration, completing the procedure.

Psalm 40:6 uses 'ears opened' as metaphor for willing obedience, echoing the ear-piercing ritual of perpetual service.

Psalm 40:8 expresses delight in doing God's will, paralleling the servant's willing commitment to remain.