13 But as to what he says, “Let them be turned and confounded,” who would not judge it to be a most righteous punishment, that they should have a turning unto confusion, who would not have one unto salvation? After this he added, “exceeding quickly.” For when the day of judgment shall have begun to be no longer looked for, when they shall have said, “Peace, then shall sudden destruction come upon them.” Now whenever it come, that comes very quickly, of whose coming we give up all expectation; and nothing makes the length of this life be felt but the hope of living.
For nothing seems more quick, than all that has already passed in it. When then the day of judgment shall come, then will sinners feel how that all the life which passes away is not long. Nor will that any way possibly seem to them to have come tardily, which shall have come without their desiring, or rather without their believing. Although it can too be taken in this place thus, that inasmuch as God has heard, so to say, her groans, and her long and frequent tears, she may be understood to be freed from her sins, and to have tamed every disordered impulse of carnal affection: as she says, “Depart from me, all you that work iniquity, for the Lord has heard the voice of my weeping:” and when she has had this happy issue, it is no marvel if she be already so perfect as to pray for her enemies.
The words then, “Let all mine enemies be ashamed, and vexed,” may have this meaning; that they should repent of their sins, which cannot be effected without confusion and vexation. There is then nothing to hinder us from taking what follows too in this sense, “let them be turned and ashamed,” that is, let them be turned to God, and be ashamed that they sometime gloried in the former darkness of their sins; as the Apostle says, “For what glory had ye sometime in those things of which you are now ashamed?” But as to what he added, “exceeding quickly,” it must be referred either to the warm affection of her wish, or to the power of Christ; who converts to the faith of the Gospel in such quick time the nations, which in their idols' cause did persecute the Church.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)