7 But who are they whom the “iniquity of their heel shall compass”? “They who trust in their virtue, and in the abundance of their riches do glory”. Therefore such sins will I avoid, and the “iniquity of my heel” shall never compass me. What is avoiding such sins? Let us not trust in our own virtue, let us not glory in the abundance of our own riches, but let us glory in Him who has promised to us, being humble, exaltation, and has threatened condemnation to men exalted; and then iniquity of our heel shall never compass us.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)