4 “That My mouth may not speak the works of men”. That nothing may proceed out of My mouth, but what relates to Your glory and praise; not to the works of men, which they do beside Your will. “Because of the words of Your lips.” Because of the words of Your peace, or of Your prophets. “I have kept hard ways.” I have kept the toilsome ways of human mortality and suffering.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)