Of all the commentators, Theodoret alone recognizes the distinction the psalmist makes between sin and impiety. The speaker, while admitting his sin, still counts himself among the faithful. The belief that sin cannot efface faithfulness is the basis for the speaker’s appeal:
Then he shows the form of the redemption: Lord, let your face shine upon your servant; save me in your mercy [31:16]: when you make your appearance, gloom is immediately lifted. Lord, let me not be confounded, because I called upon you. Let the ungodly be put to shame and cast down to Hades [31:16–17]. From this we learn that the sin is very different from impiety; hence the mighty David beseeches that he be freed from the shame caused by the sin, but those addicted to impiety be sent in shame to their death.
Although all are sinners, it may be that not all sinners put themselves in God’s hands, feeling shame before God. Those who look for relief may seek release not from divine disapproval but from the public shame that accrues from public misbehavior.