11 “For because of You I have sustained upbraiding, shamelessness has covered my face”. No great thing is that which is spoken of in “I have sustained:” but that which is spoken of in “for Your sake I have sustained,” is. For if you sustain because you have sinned; for your own sake you sustain, not for the sake of God. For to you what glory is there, says Peter, if sinning you are punished, and you bear it? But if you sustain because you have kept the commandment of God, truly for the sake of God you sustain, and your reward remains for everlasting, because for the sake of God you have sustained revilings. For to this end He first sustained in order that we might learn to sustain...“Shamelessness has covered my face.”
Shamelessness is what? Not to be confused. Lastly, it seems to be as it were a fault, when we say, the man is shameless. Great is the shamelessness of the man, that he does not blush. Therefore shamelessness is a kind of folly. A Christian ought to have this shamelessness, when he comes among men to whom Christ is an offense. If he shall have blushed because of Christ, he will be blotted out from the book of the living. You must needs therefore have shamelessness when You are reviled because of Christ; when they say, Worshipper of the Crucified, adorer of Him that died ill, venerator of Him that was slain!
Here if you shall blush you are a dead man. For see the sentence of Him that deceives no one. “He that shall have been ashamed of Me before men, I will also be ashamed of him before the Angels of God.” Watch therefore yourself whether there be in you shamelessness; be thou boldfaced, when you hear a reproach concerning Christ; yea be boldfaced. Why do you fear for your forehead which you have armed with the sign of the Cross?...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)