11 “For out of all tribulation You have delivered me”. For this cause I have perceived how good a thing is Your name: for if this I were able before tribulations to acknowledge, perchance for me there had been no need of them. But tribulation has been applied for admonition, admonition has redounded to Your praise. For I should not have understood where I was, except of my weakness I had been admonished. “Out of all tribulations,” therefore, “You have delivered me. And upon mine enemies my eye has looked back:” upon those Ziphites “my eye has looked back.”
Yea, their flower I have passed over in loftiness of heart, unto You I have come, and thence I have looked back upon them, and have seen that “All flesh is grass, and all the glory of man as the flower of grass:” as in a certain place is also said, “I have seen the ungodly man to be exalted and raised up like the cedars of Lebanon: I passed by, and, lo! He was not.” Wherefore “he was not”? Because you have passed by. What is, “because you have passed by”? Because not to no purpose have you heard “Lift up your heart;” because not on earth, where you would have rotted, you have remained; because you have lifted your soul to God, and you have mounted beyond the cedars of Lebanon, and from that elevation hast observed: and “Lo!
He was not;” and you have sought him, and there has not been found place for him. No longer is labour before you; because you have entered into the sanctuary of God, and hast understood for the last things. So also here thus he concludes. “And upon mine enemies my eye has looked back.” This do ye therefore, brethren, with your souls; lift up your hearts, sharpen the edge of your mind, learn truly to love God, learn to despise the present world, learn voluntarily to sacrifice the offerings of praise; to the end that, mounting beyond the flower of the grass, you may look back upon your enemies.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)