Friends:

 Mental Purification comes in Seven Stages!
 

1: Mental Purification by Morality.
2: Mental Purification by Meditation.
3: Mental Purification via Right View.
4: Mental Purification by overcoming Doubt.
5: Purification by Knowledge & Vision of what is Path & non-Path.
6: Purification by Knowledge & Vision of the Noble 8-fold Way.
7: Purification by Directly Experienced Knowledge and Vision.

6-WORD EXACT
Avoiding all Harm;
Doing only Good;
Purifying the Mind;
This do all Buddhas teach!
Dhammapada 183

  More on Mental Purification (Visuddhi):
  Mental_Purity, Levels of Leaving Behind, The_purpose_of_purification,
  Ability_Purification, The_8_Understandings, Immaculate_Integrity.

 

  Sources: The moderate speech on the relay wagons MN24:
  http://www.accesstoinsight.org/canon/sutta/majjhima/mn024.html
  The Seven Stages of Purification and the Insight Knowledges:
  http://www.pariyatti.com/book.cgi?prod_id=404506

Mental Purification!