22 “You know my reproach, and my confusion, and my shame”. What is reproach? What is confusion? What shame? Reproach is that which the enemy casts in the teeth. Confusion is that which gnaws the conscience. Shame is that which causes even a noble brow to blush, because of the upbraiding with a pretended crime. There is no crime; or even if there is a crime, it does not belong to him, against whom it is alleged: but yet the infirmity of the human mind ofttimes is made ashamed even when a pretended crime is alleged; not because it is alleged, but because it is believed.
All these things are in the Body of the Lord. For confusion in Him could not be, in whom guilt was not found. There was alleged as a crime against Christians, the very fact that they were Christians. That indeed was glory: the brave gladly received it, and so received it as that they blushed not at all for the Lord's name. For fearlessness had covered the face of them, having the effrontery of Paul, saying, “for I blush not because of the Gospel: for the virtue of God it is for salvation to every one believing.” O Paul, are not you a venerator of the Crucified?
Little it is, he says, for me not to blush for it: nay, therein alone I glory, wherefore the enemy thinks me to blush. “But from me far be it to glory, save in the Cross of Jesus Christ, through whom to me the world is crucified, and I to the world.” At such a brow as this then reproach alone could be hurled. For neither could there be confusion in a conscience already made whole, nor shame in a brow so free. But when it was being alleged against certain that they had slain Christ, deservedly they were pricked through with evil conscience, and to their health confounded and converted, so that they could say, “You have known my confusion.” You therefore, O Lord, hast known not only my reproach but also my confusion, in certain shame also: who, though in me they believe, publicly blush to confess me before ungodly men, human tongue having more influence with them than promise divine.
Behold ye therefore them: even such are commended to God, not that so He may leave them, but that by aiding them He may make them perfect. For a certain man believing and wavering has said, “I believe, O Lord, help my unbelief.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)