21 In your reflections therefore on yourself, think of your low estate, think of your dust: be not lifted up: if you are anything better, you will be so by His Grace, you will be so by His mercy. For hear what follows: “but the mercy of the Lord endures for ever and ever upon them that fear Him”. You who fear not Him, will be grass, and in grass, and in torment with the grass: for the flesh shall arise unto the torment. Let those who fear Him rejoice, because His mercy is upon them.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)