12 “And My eye has beheld on mine enemies”. Whom does he call his enemies? All the workers of iniquity. Do not observe whether your friend be wicked: let an occasion come, and then you prove him. Thou beginnest to go contrary to his iniquity, and then you shall see that when he was flattering you, he was your enemy; but you had not yet knocked, not to raise in his heart what was not there, but that what was there might break out. “My eye also has looked upon mine enemies: and mine ear shall hear his desire of the wicked that rise up against me.” When? In my old age. What is, in old age? In the last times. And what shall our ear hear? Standing on the right hand, we shall hear what shall be said to them that are on the left.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)